Pike River mine re-entered, just

Pike River Re-Entry Minister Andrew Little:


More than eight years after 29 men went to work at the Pike River Coal Mine and never came home, the promise to re-enter the mine drift has been honoured.

In the presence of families, experts from Te Kāhui Whakamana Rua Tekau mā Iwa-Pike River Recovery Agency completed breaching the 30m seal and successfully re-entered the Pike River mine drift. Previously scheduled for 3 May, the milestone had been delayed following a false oxygen reading from a failed sampling tube.

“New Zealand is not a country where 29 people can die at work without real accountability. That is not who we are. And that is why today we have fulfilled our promise. Today we have returned,” Minister Responsible for Pike River Re-entry Andrew Little said.

“The tragedy that took these men’s lives was the consequence of corporate and regulatory failure.

“Fulfilling the promise to do everything possible to safely re-enter is an act of justice for families who have waited for far too long.

“It is because of the families’ tireless efforts that future mining tragedies might be prevented.

“There is still much to do. We must find out what happened at Pike River. However long that takes, the recovery project will be done professionally.

“Most importantly, it will be done safely. Safety is the families’ and the Government’s bottom line. This was demonstrated when we delayed re-entry earlier this month.

“Today’s milestone belongs to the families and to the memory of their men. It also belongs to all New Zealanders, who know that going home to your loved ones is the least you should expect after a day’s work,” Andrew Little said.

Video and photographs of the re-entry have been released by the Stand With Pike Families Reference Group at www.tinyurl.com/190521pike

Background here: https://www.beehive.govt.nz/release/pike-river-re-entry


They have only just re-entered the mine. There is a long way to go.

This is a big step towards getting into the mine to investigate causes of the explosions, and to try to recover bodies, but there is a lot to do still.

I have concerns about promises being made, and expectations. The re-entry is expensive, risky, and may or may not resolve what families of the dead miners want.

 

Pike River re-entry delayed

Re-entry into the Pike River mine has been debated and delayed for eight years. Finally everything seemed to be on track for a scheduled start to re-entry today, but it was announced yesterday that this would be further delayed.

Re-entry was always going to be risky. This shows how much of a risk it is, still.

Andrew Little, Minister for Pike River Re-entry:

Safety comes first – Pike River re-entry delayed

“Yesterday unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended,” Minister Responsible for Pike River Re-entry Andrew Little has confirmed today.

“Safety has always been our first priority, and will continue to be. In these circumstances the appropriate precaution is to temporarily suspend operations.

“I back the Pike River Recovery Agency to take the time needed to fully understand the cause and significance of these new readings.

“I have spoken with Anna Osborne from the Pike River Families Reference Group. The families will be disappointed at another setback, but safety has always been their first priority too.

“The Prime Minister and I will join the families on the West Coast tonight, and families will receive a comprehensive briefing from the Agency tomorrow,” Andrew Little said.

The Agency will know more after further testing and investigative work is completed over the next week. A meeting of ventilation experts will then convene later in the month.

RNZ:  Unexplained atmospheric readings delay Pike River Mine re-entry

Mr Little told reporters that the readings of elevated oxygen levels were at the borehole, near the rockfall.

The increased levels had not been predicted, and experts advising the government could not explain it, he said.

“When you’ve got a methane-producing environment as you do there – it’s the mix of methane and oxygen that makes it dangerous – that dictates what you do to ventilate the atmosphere, so it is really about making sure that the way we respond through ventilation is going to make sure that the atmosphere continues to be respirable and there is no risk of volatility or explosion.”

There would be a range of possibilities in working to explain the readings – including that the monitoring equipment isn’t accurate – and all would have to be explored, he said.

“We’ve got a discount that possibility, it may well be that oxygen is coming in through the strata, we need to we need to confirm or clarify or discount that possibility. There will be a range of possibilities. Each needs to be explored so that we know how to respond.”

“I back the Pike River Recovery Agency to take the time needed to fully understand the cause and significance of these new readings.

Further testing and investigative work will be completed over the next week and a meeting of ventilation experts will then convene later in the month.

Pike River Recovery Agnecy head Dave Gawn told media in Greymouth the delay was due to an unexpected reading in the gas monitoring.

He said safety was key.

“Dinghy and I would have no hesitation calling stop to the proceedings,” he said.

Dinghy Pattinson – the Pike River Recovery Agencies chief operating officer – said two days ago the agency started a breaching operation of a concrete seal at the start of the mine.

But at the same time they found unusual gas readings at a borehole monitoring point (at borehole 51) deeper in the mine, above rockfall.

He did not know what caused the reading, and had not seen it before.

The cause of it could be something as simple as a damaged tube, he said.

To figure out the cause the agency had lowered another gas detection tube down the same borehole.

But Mr Pattinson said the re-entry would definitely happen, he just could not say when.

They can’t afford to risk another catastrophe in the mine, but there will never be no risk.

RNZ:  Tears shed at news Pike River re-entry would be delayed

Pike River families shed tears when the news came through that today’s re-entry attempt would have to be suspended.

Hopes raised and dashed again for the families who have been pushing for re-entry.

Some want the remains recovered. Some want the cause of the explosions found. Both could be very difficult to achieve.

Is it worth any risk?

 

 

National backs Pike River mine re-entry

The National Opposition have said they now support re-entry into the Pike River mine as they believe it can be done safely.

NZ Herald:  Politics off the Pike River table as National backs re-entry

The National Party is accepting advice that the Pike River re-entry can now be done safely, taking politics off the table on an issue that has been a bitter political battleground.

Yesterday, the party’s Pike River recovery spokesman, Mark Mitchell, met with the Families Reference Group – which represents more than 80 per cent of Pike River victims’ families – and told them National supported the re-entry plan.

Afterwards, Mitchell told the Herald the party’s position had always backed a re-entry as long as it could be done safely, but it is the first time National has told the families’ group it backs the plan.

“The advice now is that we can get in there, and we completely support that.”

As far as I can find rep-entry is planned to begin on 3 May:

Minister Responsible for Pike River Re-entry Andrew Little has announced that in light of the current state of preparations, the scheduled date to commence re-entering and recovering the access tunnel to the Pike River Mine (the drift) will be Friday 3rd May.

“Since I announced on 14 November 2018 that the project will proceed, there has been an incredible amount of preparation to get ready for re-entry. This has included preparing bridges for heavy loads, installing a nitrogen plant, upgrading the power supply, laying many kilometres of piping for the nitrogen, drilling more boreholes, installing monitoring equipment, and purging and ventilating the drift.

“As well as this, staff have been trained on working in a forensic environment. Worksafe have been reviewing all aspects of the planning, risk assessments and supporting documentation, in order to ensure the re-entry plan is safe.

https://www.beehive.govt.nz/release/pike-river-mine-re-entry

 

Safety concerns over Pike River mine re-entry

It’s not surprising to hear that there are safety concerns over the planned re-entry of the Pike River mine. Police will not be in the initial re-entry, limiting the chances of finding forensic evidence about the cause of the explosions and the fate of the 29 miners who were killed there in November 2010.

Stuff – Pike River re-entry: Police won’t be among first inside mine after risk assessment raised safety concerns

Police will not send staff in with the first Pike River mine re-entry team following a risk assessment.

The Government gave re-entry plans the all-clear in November. Minister Andrew Little said at the time a number of dangers still remained, but extensive advice had shown re-entry to the drift using the existing access tunnel of the mine would be “by far the safest option”.

Police said in September they would enter the tunnel only if the mine re-entry plan was approved by both the Police Commissioner and an independent review.

The police spokesman they were continuing to discuss the re-entry plan with the Pike River Recovery Agency, mine experts and Worksafe. The most recent discussion with experts took place on Friday, and discussions were “ongoing”.

“Police will go into the mine when we know it is safe and we know that there is no risk to our staff, or any others who are in the mine with us.

There will always be some risks going back into the mine. The police will presumably have to assess whether the potential benefits of investigating inside the mine justify the risks.

“This is a complex, technical process and we are absolutely committed to supporting the work to re-enter the mine, just as we are to ensuring safety of our staff. We are currently developing training to be given to staff, and have established a dedicated team to support the police role in the re-entry operation. This work will continue in the coming weeks.”

Christchurch Detective Senior Sergeant Grant Collins has been seconded to represent police in the Pike River Recover Agency. He could not be contacted for comment on Tuesday.

He said in September if re-entry was achieved, police would complete a scene examination, recover any bodies, and complete any other processes required on behalf of the coroner.

Police decided in 2013 to leave the criminal investigation open until the scene could be examined.

Any new evidence they found would be used to determine whether charges could be laid.

I really doubt whether evidence can be found that would support charges being laid. I don’t know what they expect to find in there.

Not all Pike river families approve of re-entry

‘Pike River families’ has often been put forward as one unified group wanting re-entry to the mine and recovery of the bodies, but at least one family opposes the re-entry plan, calling it disgraceful.

Recent news reports refer to the families collectively:

Andrew Little on Pike River: ‘Re-entry is about fulfilling a promise to the families’

“Re-entry of the Pike River Mine will proceed. To the Pike River families, to New Zealand, we are returning.”

Pike River relatives on mine re-entry: It’s a ‘truly amazing day for our families’

Friends and family of the 29 men killed in the Pike River Mine disaster say an agreed plan to re-enter the mine is a historic moment of truth and justice.

Sonya Rockhouse, who lost her son Ben in the disaster, told Morning Report the change of government had made a huge difference to the families’ campaign and the previous National government had failed them, she said.

Bernie Monk, who also lost a loved one, said it was a proud day for all Kiwis.

Anna Osborne said it was a historic moment for truth and justice and that the announcement was a “truly amazing day for our families”.

“We fought really hard for our men for a really long time and today, this is a victory for our families,” she said.

“This is a victory for the little people of New Zealand.

Pike River Recovery Agency (Government website): Family Reference Group

The Pike River Recovery Agency works in partnership with the Family Reference Group, who represent the overwhelming majority of the Pike River families.  Here they introduce who they are:

‘Stand With Pike’, the families of more than 80% of Pike victims, have fought hard for answers as to why this happened or, more to the point, why no-one intervened to stop it.

24 of 29 is 82%, so that means up to five of the families are not represented.

And one of those five has spoken up – Mother of Pike River victim: Re-entry plan ‘disgraceful’ (RNZ):

Christchurch mother Marion Curtin says she was left sitting by her phone feeling raw after the announcement of the Pike River Mine re-entry yesterday.

Her son, Richard Holling, never came home after the November 2010 tragedy, but she wanted it to stay that way.

Some people might assume that all 29 affected families considered yesterday’s news as a “victory,” she said, but she was one of the silent many who disagreed.

She said the plan was an “appalling” waste of $36 million.

“I’m just so disappointed. I couldn’t believe that cabinet would sign this off,” she said.

Especially given the lack of certainty, she said, with nobody able to tell her exactly what the mine recovery experts would be looking for.

“I see it as sacrilege, really. To go in fossicking around for remains… to go in just to see what they find – I think it’s just disgraceful,” she said.

Ms Curtin loathed the fact it had become so political. She said the months leading up to last year’s election were especially challenging.

“Some people liked that… the politicians climbing on board. I certainly didn’t. That was my son’s death they were playing with.” she said.

While yesterday’s news had been extolled as a “huge victory” and a relief for the people in Greymouth, Ms Curtin did not feel this way and refuted the idea that she was in the minority.

Different people have different ways of dealing with grief. I’m not sure that that is well enough recognised by the recovery agency and the politicians promoting re-entry.

Following the loss of her son, Ms Curtin said said she had just been trying to get on with her own life.

“I remember Richard with love every day. But for me a good day is when I don’t hear Pike River mentioned. I don’t dwell on Pike River.”

Repeatedly bringing the tragedy up in the news can be hard for some people.

And if the re-entry ever gets to the stage of finding bodies, can they respect the wishes of some families, any families, who don’t want ‘fossicking around for remains’?

 

‘Closure’ may be elusive in Pike River re-opening

The Press Editorial: Pike River decision is a victory for justice

The decision to re-enter the Pike River Mine in early 2019 has been a long time coming and does not have universal public support. Some see it as merely a triumph of public relations and emotion, or of election promises over tough realism.

But they are arguably a minority voice.

That is certainly arguable, with nothing to support this claim of minority dissent.

While it is clear that a lot is at stake for a Government that made a commitment to the Pike River families – and particularly for Pike River Re-entry Minister Andrew Little, who has campaigned so vigorously – most New Zealanders will be both sympathetic to the suffering of those family members who support re-entry and will also see the value of answering questions about a disaster that killed 29 men on the West Coast eight years ago.

Politicians are bad at overusing unsubstantiated ‘most New Zealanders’ claims. While editorials are opinions it’s disappointing to see a major newspaper prop up their views with assumptions.

Those who argue that the grieving families should accept their losses and move on are therefore overlooking the fact that justice has been elusive in the Pike River case.

Crap. Some maybe. But I don’t overlook the justice aspect. What I think though is that the re-entry may struggle to do justice to identifying causes as much as it may struggle removing the remains of the miners (especially all the miners).

For the families who support re-entry, led by representatives Anna Osborne, Sonya Rockhouse and Bernie Monk, the announcement of the re-entry speaks to a dogged determination that is both a tribute to the memory of lost family members and a wider commitment to truth over political and bureaucratic obfuscation.

As Dave Gawn has suggested, there is a good chance there will no bodies in the drift of the mine. If that happens, you can expect to hear a familiar chorus of voices calling the re-entry an expensive stunt. But it will be just as important to learn whether evidence has been gathered that can progress a criminal case and might even lead to the apportioning of blame that the doomed mine’s former manager seems so eager to minimise.

I think there is a high chance of disappointment in the first attempt at re-entry. What then?

NZ Herald editorial: Expensive Pike River re-entry plan does not go very far

There was never much doubt the present Government would grant the wish of Pike River families to re-enter the mine as far as that may be done safely.

The fact those two were able to walk out of the mine after the explosion suggests no others were in the tunnel, but for some of the families, as the past eight years have proved, hope springs eternal.

If the re-entry discovers no human remains, there is at least the possibility forensic evidence will be found pointing to the cause of the first explosion and permitting those responsible to be held personally to account at last for 29 deaths.

A royal commission of inquiry produced damning conclusions of the cause of the disaster based on testimony of those who knew the mine, and the mine insurers have made a payout to the families, but it is possible something found in the tunnel will provide a clearer explanation, possibly even an indictable one.

I think it’s unlikely much in the way of useful forensic evidence will be found in the initial re-entry.

On these remote possibilities the Government is staking $36 million, an extraordinary increase on the $7.2 million plan put to the previous Government just five years ago. And yet the minister in charge, Andrew Little, has obviously chosen the cheapest of three options put to him by the Pike River Recovery Agency.

Little and his recovery agency do not sound sure of what they will be able to do beyond the second chamber only 170m into the 2km tunnel. Little said, “There is a lot we don’t know and will not know until we are confronted with the situation as we find it”.

He added, “This will require agile thinking, the courage to say if we are uncomfortable, the preparedness to re-assess, reset and re-plan when necessary, and knowing when to call it quits”.

Clearly a lot could go wrong.

Hopefully nothing major will, go wrong, but the chances of everything going right may be slim.

But the families that have been pressing for a re-entry for eight years have been rewarded for their persistence.

They managed to successfully play political pressure game.

They have never sounded hopeful that a recovery effort could get further than the rockfall. They must accept this plan could get that far and find nothing of their loved ones. If nothing else, it surely provides the “closure” they need.

Really? I’m not clear on what ‘closure’ actually is (apart from closure of the mine which they opposed). I think it probably means different things to different people.

If it means making everyone happy I’m not optimistic.

Plan to re-enter Pike River mine announced

This announcement is just being made:

Stuff:  ‘We’re going in’ – Government unveils decision to re-enter Pike River Mine

The Government has given the all-clear to re-enter Pike River Mine, to retrieve the bodies of the 29 men who died there in 2010.

While a number of dangers still remained, Little said extensive advice had shown re-entry using the existing access tunnel of the mine would be “by far the safest option”.

Little said it would be an “extraordinarily complex” undertaking, but the process to make it safe had been robust.

“Safety has been our paramount concern throughout this planning process, and supported wholeheartedly by the Pike River families”.

The operation also had the support of the police.

“With their support and advice the drift tunnel will be thoroughly examined through to the roof fall area.”

Work to prepare the mine was already underway. That included venting methane from the mine, pumping nitrogen into the mine, and filling the drift with fresh air.

Additional boreholes would have to be drilled, and that work would get under way immediately, said Little.

“The advice I have received indicates that it is likely to be round February before the re-entry proper gets underway, by breaching the 30m seal.”

I understand that this is a big deal for some of the families of miners who were killed.

But I really wonder whether this is a sensible thing to do. And I wonder what will be achieved, apart from perhaps the removal of some or all remains.

 

Pike River re-entry may be further delayed

Yesterday from Andrew Little:  Significant step in Pike River drift re-entry

Minister Responsible for Pike River Re-entry Andrew Little has received the report on re-entering the Pike River drift following nine months of intensive work by Te Kāhui Whakamana Rua Tekau Mā Iwa Pike River Recovery Agency.

The Agency has identified three safe and feasible re-entry options to recover the drift:

  • Drive a small tunnel to create a ventilation circuit;
  • Single entry, using the existing main drift access tunnel as the sole means to ventilate the main drift;
  • Single entry with a large diameter borehole.

“I want to acknowledge the work of the Pike River Recovery Agency in getting us to this point. Safety of everyone is fundamental for re-entry, as is the care needed to forensically examine what happened at Pike River to ensure it never happens again.

“I am satisfied that the Agency has been robust in developing the options. Workshops have included technical experts, and partners including New Zealand Police, Mines Rescue, WorkSafe and the Department of Conservation.

“The Pike River Families and their representatives have been also included at every stage. The families have shown extraordinary patience and tenacity, and their contribution has been crucial.

“The explosion at Pike River Mine on 19 November 2010 was a national tragedy. Today we are one step closer to – finally – bringing closure to the families.

“It is my responsibility as Minister to carefully weigh the options, alongside Rob Fyfe’s independent advice. I take that responsibility very seriously.

“I do not intend to make further public comment before a decision has been taken, which is expected to occur by the middle of November,” said Andrew Little.

Little has also talked to NZ herald about it: Andrew Little receives report on options for Pike River mine re-entry

It is looking less likely that any re-entry to the Pike River mine drift will happen before Christmas, Pike River Re-entry Minister Andrew Little says.

Little told the Herald today he would make a final decision on whether it was even feasible to re-enter the drift after reading the report and receiving advice from independent ministerial adviser Rob Fyfe.

Little told a parliamentary committee in June it was possible re-entry could be started by the end of this year but today he pulled back from that.

“I understand that is looking less likely now and it would be the early part of next year,” he said.

But he would give a better timeline on the operation to breach the seal if and when he announced a decision to go in.

“When they’ve had the various experts, including the families’ experts, come together, the conclusion of each of those sessions is that this is feasible. But I’ve got to be satisfied,” Little said.

Little has also yet to ask Cabinet to ask for $10-15 million on top of the up to $23m already budgeted for the recovery.

Other ministers have said that ‘priority’ policy implementation has to wait for the next budget.

This is taking a long time and a lot of money. I really wonder if it is all worth it – and worth the risk. Sure, some families want the remains of miners removed, but it is hard to see whether that will change much.

There are also hopes that the cause of the explosions will be found but that could require a far more extensive investigation than is practical.

Pike River re-entry costs escalate

A ‘concept plan’ for re-entry into the Pike River mine to recover miners’ bodies has been presented to their families by the Minister responsible for Pike River re-entry Andrew Little (actually three alternative options), but with that is a bigger than previously estimated cost.

RNZ: Pike River re-entry: ‘Concept plan’ presented to families

A plan for re-entering the drift of the Pike River Mine has been presented to victims’ familes in Greymouth this morning.

The plan is being described as a “concept plan” with more detailed planning to follow if it is approved.

Minister responsible for Pike River re-entry Andrew Little, and Pike River Recovery Agency chief executive Dave Gawn have been talking to the relatives of the 29 men killed in the mine in 2010.

Mr Little said the families were now discussing the plan and he hoped to give it the go-ahead on Monday.

However, he said he expected they would approve the concept plan.

“My sense is the families are really happy with the level of work that has been done, the quality of ther work. They seem pretty satisfied with it … They’re keen for the project to continue to make progress, so that we re-enter the drift and recover as much as we can.”

RNZ:  Pike River Mine re-entry narrowed to three options

The planned re-entry to the Pike River mine has been narrowed to three options.

Mining specialists, Pike River Recovery Agency staff and family members of the 29 men killed in the 2010 blast were on the West Coast for a second workshop aimed at coming up with a plan for manned re-entry of the mine drift.

A panel of technical experts will now shift the focus to three scenarios which are now being developed further.

The scenarios include:

  • building a new two by two-metre tunnel around 200m long;
  • drilling a large diameter borehole;
  • re-entering the main drift as it is with no second means of egress (exit).

The aim is to try and find out what happened in order to prevent any further tragedies, to give the families closure and where possible, retrieve any remains found in the drift, the agency said.

Dinghy Pattinson, the recovery agency’s chief operating officer, said he was confident they would get back in.

“Any mining activity has dangers or risks involved, so it’s a matter of just identifying those risks throughout the whole process and having your controls in place,” Mr Pattinson said.

“If there was any real danger then that would be a show-stopper, so at this stage all the risks identified – I feel confident we can manage them.”

Recovery Agency chief executive Dave Gawn said they had made bigger steps during this workshop.

“We still anticipate entering the mine before the end of the year, and we still think that’s achievable. This workshop is only step number two in a number yet to take,” Mr Gawn said.

He said among the steps was a detailed risk analysis of the preferred options.

It sounds like they are still far from certain how to get back into the mine, how risky it would be – and how much it would cost, even they they don’t yet know how they will do it.

Stuff: Pike River re-entry could cost $12m more than $23m budget, minister says

The plan to re-enter the Pike River mine could cost up to $12 milllion more than the $23 million budget, Stuff understands.

The Government had budgeted $7.6 million a year for three years, totalling up to $23m, for the Pike River Recovery Agency and re-entry to the mine.

When asked if he had told Cabinet the agency would need up to $12m more, Little said one of the options could cost up to that amount, but others would be less than that.

“We won’t know exactly what the figures are until more detailed work has been done.

While there remains a lot of doubt about how a re-entry would be achieved the expected cost seems to keep escalating.

I understand that some families really want the bodies of some miners recovered (some families don’t see the need).

What if the option chosen is the more expensive one – $35 million – and they get into the mine and they can’t find or can’t recover all of the bodies? What if bodies unrecovered are from families that most want them recovered? What then? Keep spending until they find and recover them all?

What if they can’t find out the cause of the explosions?

 

Chinese space station falling soon

The Chinese space station Tiangong-1 was blasted into orbit in 2011. In March 2016 control was lost, and since then the 10 metre long station has been gradually losing altitude. It is expected to burn and possibly crash in the next day or two, but it is uncertain exactly when, and where.

Image result for tiangong 1

The possibilities:

It sounds like we are safe as far south as Dunedin, and most and probably all people around the world will be unaffected.

It is unprotected by heat shields so will mostly or completely burn as it drops into the Earth’s atmosphere. This could be spectacular if you can see it – and with streaming telescopes that should be easy wherever it happens.

Thanks to the Virtual Telescope Project and the Tenagra Observatory, people can see it live –click here to watch.

LiveScience: Here’s How to Watch the Chinese Space Station’s Uncontrolled Plunge to Earth

The Chinese space station Tiangong-1 is plummeting back to Earth this weekend, and anyone with an internet connection can watch the fiery demise live online.

Tiangong-1 is expected to re-enter Earth’s atmosphere sometime between late Saturday (March 31) and late Sunday (April 1).

With our time difference in New Zealand add half a day or so to that, so Sunday-Monday.

It also remains true that it is not a danger to you or anyone else, because the Earth is very big and still mostly pretty empty, and the station is very small in the scheme of things. And the odds of getting hit by a piece of the space lab that manages to survive the fiery re-entry into our atmosphere are incredibly low.

The Conversation: Tiangong-1 crash: why it’s so hard to predict where space debris will land and what can be done about it

While experts have been aware that this would happen for more than a year, there has been huge uncertainty around the exact timing. As the station’s orbital altitude has decreased, however, this uncertainty has gradually reduced and it is now possible to determine that it will deorbit within a few days.

Most of the 8.5-tonne station will burn up and disintegrate as it passes through the atmosphere, though some debris may hit Earth.

We cannot actually predict the time and place of Tiangong-1’s potential impact on Earth, despite it being only 200km above us.

Why is it so difficult, and will science one day help us nail such predictions?

Newton’s laws tell us that satellites orbit the Earth in perfectly circular or elliptical orbits, repeating their path again and again (assuming that gravity is the only force acting on them). However, this is not true at low altitudes, say below 1,000km, because the satellite is then moving through the Earth’s atmosphere. This causes “aerodynamic drag” (air resistance) – a force that opposes the satellite’s velocity, which effectively turns the orbit into a downward spiral towards the Earth’s surface.

The spacecraft’s velocity is easy to measure fairly accurately using observations. However, the other parameters are highly uncertain – making it difficult to determine Tiangong-1’s path. For vehicles such as cars and aircraft, C can be estimated theoretically or with computational fluid dynamics and measured experimentally in a wind tunnel. The main problem here is that Tiangong-1’s shape is complex, and the object is uncontrolled and tumbling chaotically, resulting in a constantly changing airflow.

The other unknown is the density of the atmosphere, which decreases with altitude. However, particularly at high altitudes, this varies due to a number of unpredictable factors – the most important of which is solar activity.

Another important factor is that the satellite will disintegrate and burn during the final phases of reentry, adding further uncertainty to all terms of the drag formula.

One thing is certain – there will be plenty of coverage of the burn online and on TV, and if any remnants crash the location is likely to be known and closely examined.