ATV-5 seen during ISS flyunder on 8 August. Credit: ESA/NASA

ATV-5 seen during ISS flyunder on 8 August. Credit: ESA/NASA

ATV-5 mission manager Massimo Cislaghi sent us this informative update on ATV-5’s planned reentry that will take place next month:

As promised with my previous mid-mission report of 7 November I come back to you for a short update, this time focusing on the preparation of the end of the mission, which also means (sigh …) the end of the entire ATV Programme.

Lidar view of ISS. Credits: Jena-Optronik

LIRIS Lidar view of ISS. Credits: Jena-Optronik

A novelty introduced for ATV-5’s docking was the LIRIS demonstration including a special ISS “fly-under”. With that finished we are now concentrating our efforts towards the implementation of another totally new operation during Georges Lemaître’s reentry, which deserves few words of background.

Mir. Credits: NASA

Mir. Credits: NASA

When the International Space Station reaches its end of life, the big orbital complex will have to be de-orbited, similarly to what was done with space station Mir in 2001. The amount of energy required to brake more than 400 tonnes of hardware to have it captured by Earth’s gravity, is not and will not be stored onboard at that time. This means that the Space Station’s speed will be reduced slowly so its atmospheric reentry is expected to occur in a path that is not as steep as one would like ideally. We call it a “shallow reentry”. The operational and safety implications of such a manoeuvre are enormous. It will be necessary to predict when and how the International Space Station will start its fragmentation, whether explosions will occur and how fragments will behave. Will all the fragments be captured by Earth’s gravity or will some remain in orbit? How will their shape affect their trajectory as they hit denser and denser atmosphere? Which fragments will burn during reentry and which ones could touch Earth’s surface, and where?

Computing these questions require a huge analytical effort, relying on mathematical models that need to be validated somehow, in particular those related to reentry trajectory transitions from 120 to 90 km altitude. This is why the International Space Station Programme, and NASA in particular, thought that ATV-5’s reentry could be useful for this purpose. Even if ATV-5 is much smaller than the Space Station, its shape and mass can be considered similar to each Space Station module, as they are expected to separate during reentry as the dynamics will cause nodes linking the models to rupture.

ATV-4 reentry in 2013. Credits: ESA/NASA

ATV-4 reentry in 2013. Credits: ESA/NASA

NASA asked us to radically modify of Georges Lemaitre’s atmospheric reentry, and we were happy to accept. Instead of the traditional, steep path of the previous four ATVs, ATV-5 will follow a much shallower one, to make it as close as possible to the predicted Space Station reentry trajectory. As you can imagine, this modification has triggered quite a lot of non-standard work, mostly at the ATV Control Centre. In particular the entire operational post-docking strategy had to be redefined nearly from scratch and compliance with all safety requirements had to be verified again, especially knowing that a lower reentry angle means a higher ATV explosion altitude, a larger dispersion of fragments and eventually a longer reentry over Earth’s surface.

This delicate process is now very close to a positive accomplishment, pending the approval of the Re-entry Safety Review Board that will gather by the end January. In parallel many monitoring means are being readied to get as much data as possible during the few minutes we are interested in. In practice we will have:

  • ATV Break-up Camera. Credits; ESA

    ATV Break-up Camera. Credits; ESA

    Two instruments, one from ESA (the Break-Up Camera) and another from NASA (the ReBR-W) will be installed by ISS astronauts in ATV-5’s Pressurised Module shortly before undocking. They will capture video and temperature and acoustic data, which will be transmitted to Earth via Iridium satellites. A third instrument from JAXA was also planned, but it was unfortunately lost on the Cygnus launch mishap in October.

  • Several cameras on the Space Station will be pointed towards ATV-5 as it flies below. This will require ATV-5’s orbit after separation to be precisely phased with the Station’s, so that it will cross the 120/90 km transition zone exactly below the orbital complex.
  • A NASA DC-8 plane will host an ESA-led airborne observation campaign, with several instruments observing ATV-5’s reentry very near the reentry (but not too close…).
  • Finally, a large series of ground radars, telescopes, and so on from scientific organisations will observe the vehicle, mostly in Australia and New Zealand, since these will be the last two countries Georges Lemaître will fly over before its final splashdown.
Artists impression of ATV-5 breakup and reentry. Credits: ESA-D. Ducros

Artists impression of ATV-5 breakup and reentry. Credits: ESA-D. Ducros

Apart from the instruments on ATV-5 the other observation equipment require specific illumination conditions during the most interesting part of the reentry to draw maximum benefit from this unique opportunity. Due to this need it has been determined that the optimum day for the final dive of Georges Lemaitre will be 27 February 2015, with a backup on the next day. The undocking from the International Space Station will take place a number of days before that to allow ATV-5 to rephase with the International Space Station, but not too many days before, or else the BUC’s battery could be discharged. Some discussions are currently ongoing at Flight Planning level, to try and freeze the undocking date, with 14 February as a target (even if somebody commented that St.Valentine’s day is not the best suited for a separation …).

That’s it, in few (well, not so few …) words. For the rest, I can only repeat what I wrote few weeks ago, that the Georges Lemaître continues to be EXCELLENT. Cargo off-loading and trash loading is continuing according to plans, which might be considered as a routine activity, but as everybody knows in our business, routine does not exist. In particular our ATV Control Centre colleagues are kept constantly busy.

For the first time since the beginning of the ATV Programme the ATV Control Centre was kept busy during the end of year and I address this at first instance to them, and then of course extend to everybody else my

Best Wishes and Happy New Year 2015 !

Felice Anno Nuovo 2015 !