Ariane 5 rocket is contracted to launch JWST. This rocket has approximately one failure out of every fifty launches (excluding minor failure). JWST has already taken many years and it is next generation telescope.

In case of failure after the launch, will the payload remains uncharred and safe? Is there any failsafe condition (for example a Launch Escape System) that will be undertaken by Ariane 5?

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  • $\begingroup$ different but related: Will the James Webb Space Telescope be insured against launch failure? $\endgroup$
    – uhoh
    Commented May 14, 2020 at 6:12
  • 3
    $\begingroup$ JWST is rather fragile structure. Maybe in launch configiration (packed) it technically can survive LES acceleration (usually about 20 g), maybe not. But much more hard to survive Earth contact at landing, even with parachutes + airbags, I think. And it's absolutely impossible to avoid close-to-irreparable contamination by the environment after landing.So, many problems with this idea. $\endgroup$
    – Heopps
    Commented May 14, 2020 at 10:26
  • $\begingroup$ Minor clarification: the Ariane 5 rocket is not technically "contracted", but rather part of the ESA contribution to JWST. $\endgroup$
    – user24033
    Commented May 15, 2020 at 19:00
  • $\begingroup$ Number of failures / number or flights is not an accurate way to mesure the probability of future failures $\endgroup$
    – Antzi
    Commented May 17, 2020 at 0:29

1 Answer 1


There is no* safe condition used by Ariane 5.

It is not common to use Launch Escape Systems for UNmanned flights. Actually the hardware of a spacecraft is not as costly as you may think, the development itself is driving the costs. So usually there are Flight Spare Units (Wikipedia Flight Spare) of the spacecraft, sometimes even (nearly) assembled. If a launch failed, you put the spare parts together and try a second time. You just have to pay the man hours to put everything together. No additional development, no new coding, no manufacturing of new parts.

Of course Ariane-Space and the JWST-Guys have contracts if there are penalties payments due or have insurances to cover some damage. But in the end, that's cheaper than trying to save the (unmanned) payload.

*) I mean, there are several safe mechanisms, but not to save the payload, if there is a total loss of the rocket.

EDIT: At least for some parts of JWST, information about Spare Models are available: A CRYOGENIC ROTATING ACTUATOR Some Prisms for "MIRI" REFOCUSSING MECHANISM

  • $\begingroup$ Is there, in fact, a spare JWST or parts to make one. I think not. $\endgroup$ Commented May 14, 2020 at 11:56
  • $\begingroup$ A one minute search in google for "james webb space teleskop flight spare unit" results in: at least some spare mirrors are shown. A two minute search in google for "jwst flight spare" results in a paper how to store existing flight spare detectors. So I think yes. The space missions I worked for always had flight spare models, Rosetta Lander even had two, and some instruments had been exhanged before flight. FSM was obligatory for all NASA and ESA missions and I do not belive, they changed this policy. $\endgroup$
    – CallMeTom
    Commented May 14, 2020 at 12:25
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    $\begingroup$ Since the question is specifically about JWST, if you believe there is a real possibility of a spare existing or being built, that would be a good addition to your answer, if you can back it up. Since it's the whole rationale for said answer. $\endgroup$ Commented May 14, 2020 at 12:27
  • $\begingroup$ @CallMeTom Im guessing it would be a hard sell to anyone to spend the next 3 years building an identical JWST replacement when the hardware is already a decade behind the state of the art? It must be really tempting to say "yeah, but with a little bit of investment here and there we get so much more" and there goes another 5 year delay :D $\endgroup$
    – Moo
    Commented May 15, 2020 at 4:00
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    $\begingroup$ @Moo: rebuilding from spare parts means: take your permanent employed staff at Noordwijk or whereever the NASA pendnat is, take your LEGO-like building instruction put it together, make basical structural test (low-level shaking) and put it on a rocket. "a litte more inverstment here" means: hire new fixed-term contracted personnel in universities, make new thermal, EM and mechanical tests, write new procedures. Everythng on instruments- assemblies- and S/C-level. Shaking identic copies till they broke, reiterate the concept...ops, a new SpaceCraft appears ;-) ...10 years later $\endgroup$
    – CallMeTom
    Commented May 15, 2020 at 4:36

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