19 June 2011 04:51 ET
Late on Tuesday (GMT), a huge fireball will streak across
the skies over the Pacific Ocean.
Not many will get to see it; it will be over an uninhabited part of the
world, and ships and planes have been warned to steer clear of the area.
The event is the return from orbit of Europe’s
space freighter, ATV-Johannes Kepler.
It has completed its mission at the International Space Station (ISS) and
it’s now time to come home.
The freighter took up more than seven tonnes of fuel and other supplies to
the orbiting outpost, but for its return it has been packed with the platform’s
Little of the ship or this waste is actually expected to make it all the way
to the surface of the Pacific Ocean. Most will simply vaporise in the intense
heat generated during the descent through the atmosphere.
This is the second time a European freighter has made the fall to Earth. In
2008, the maiden vessel, Jules Verne, did exactly the same thing.
occasion, its brilliant path across the sky was observed
by US and European space agency research planes. Their observations produced
some remarkable video and some of the most detailed analysis ever done on what
happens to a spacecraft when it breaks up on re-entry.
That analysis is still ongoing; scientists continue to debate precisely which
components broke away, and when. But they have a broad picture.
“The break-up created a big jigsaw puzzle of pieces,” said aircraft observing
campaign principal investigator and meteor astronomer Peter Jenniskens of the
Seti Institute and Nasa Ames.
“We analysed the colours of those fragments to figure out their composition.
The two participating airplanes provided depth perception to trace the fragment
paths,” he told BBC News.
Falling space debris
- Hardware re-enters at shallow angles (<1 degree)
- Some 50 items weighing >1 tonne re-enter a year
- Major break-up occurs about 80km altitude
- 10-40% of dry mass on orbit will survive
- Debris spreads over long, thin “footprints”
- It can be a hazard to people and
Jules Verne was a 13-tonne object when it came back. It engaged the top of
the atmosphere at an altitude of about 120km, travelling at about 7.6 km/s.
As it plunged deeper and deeper, it started to tumble. The solar panels were
the first obvious casualties – ripped from their mountings about 83-84km up.
As the ship progressed downwards, it got hotter and brighter, creating a
multi-coloured fireball – a shower of blues, yellows and oranges.
Spectrometers on the “chase planes” picked up in this light shower the
signatures of the various materials in the ship burning off.
“Some fragments show paint peeling off; others show aluminium melting. We
even see the main lithium batteries fall apart, creating four dots of bright
pink light,” said Jenniskens.
If you watch the video on this page, you can pick out a couple of key moments
that have generated much debate inside the research team.
The first is a sudden brightening at about 6″ into the video. This is a major
fragmentation event at 75km altitude.
The ship lets go, severing into two big pieces. It breaks into three large
chunks shortly afterwards.
Interestingly, the major fragmentation event does not appear to be the result
of a fuel explosion.
“It looks as though it should be,” said Jenniskens, “but if it were, there
would have been a lot of carbon and hydrogen visible to the instruments.”
You’ll see one bright item move ahead of the debris field. It’s very
distinctive, and scientists detected the presence of lithium; a spent battery,
Jules Verne’s debris train eventually disappears from view at about 31km
altitude. The team cannot say for sure how much material survived to the
surface, but it’s thought very little splashed down.
“The results should provide engineers with better tools to understand the
re-entry physics of such complicated spacecraft,” said project manager Jason
Hatton of Esa’s Estec facility in Holland.
“That in turn will feed back into better spacecraft design, especially of
thermal protection systems, or heatshields, and an improvement in the models
that are used to assess debris footprints.”
On occasions, spacecraft or old rocket stages will come back to Earth in an
uncontrolled manner over land, and safety concerns demand that we have a good
idea of where chunks of metal might hit the ground.
Kepler’s return will not be subjected to the same level of analysis.
The type of observation campaign mounted for Jules Verne takes much
preparation and analysis. Instead, Kepler has a “blackbox” aboard.
This Re-Entry Breakup Recorder (REBR) will record temperature, acceleration,
rotation rate, and other data as Kepler tumbles through the atmosphere.
In the latter moments of re-entry, it should break free from the main debris
cloud, right itself and then make an Iridium satellite phone call to downlink
everything it has learnt.
The REBR is not intended to survive its impact with the ocean, although –
remarkably – the one fitted to the returning Japanese space freighter, HTV-2, in
In future, many spacecraft and rockets will carry these devices, especially
as they incorporate more composites. There is very limited data on how these
materials behave when they fall to Earth.
Recommended: There is an interesting
behind-the-scenes video of the Jules Verne descent which ties together what
was happening inside the chase planes with what the observers were seeing
through their windows.
ATV-Johannes Kepler was launched on February 16th, 2011 at 21:51 GMT according to http://en.wikipedia.org/wiki/Johannes_Kepler_ATV
February 16th, 2011
2 + 16 +2+0+1+1 = 22 = ATV-Johannes Kepler’s life lesson and personal year = Look before you leap. You’ve gotta be kidding me.
22 year + 6 (June) = 28 = ATV-Johannes Kepler’s personal month (from June 16th, 2011 to July 15th, 2011) = Powerlessness.
28 month + 21 (21st of the month on Tuesday June 21st, 2011) = 49 = ATV-Johannes Kepler’s personal day = Be careful what you wish for – you just might get it.