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Comment by jballanc | Hacker News Reader

While not a huge deal in that both satellites seem to have reached an orbit (even if not exactly the desired orbit), it's worth noting that NASA picked the Ariane 5 as the launch platform for the JWST at least partially because of its extreme reliability. It would be a damn shame to lose an $8.8B instrument in development for over 23 years due to a launcher malfunction.

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There is a docking ring on JWST, so it could be reboosted to a proper orbit if there's a problem with the launch.

A Dragon spacecraft (which will launch uncrewed with a docking capability sometime this year) or just some satellite bus with an NDS docking ring, should be capable of boosting it if there's a minor performance shortfall like this launch. $150 million, I would guess, would be the cost to address a minor performance shortfall like this. That's not too bad since JWST is a $10 billion spacecraft.

It should be pointed out that the electric-propulsion-equipped spacecraft actually launched will have no trouble reaching the correct orbit, it'll just take 4 weeks longer than planned.

The performance shortfall, based on guesses of the electric propulsion performance and the 4 weeks delay, is probably around 50 to 100m/s. JWST has a budget of around 150m/s, so JWST would, in principle, be capable of moving itself to its planned orbit, but this would signficantly impact its on-orbit lifetime (or require fancy mission planning... I'm always impressed by how clever mission planners can squeeze water from a rock when a problem like this occurs).

So JWST itself may actually have enough propellant in case this problem occurred again, and there is a docking ring on JWST that could, in principle, be used for reboosting it.

It should be pointed out that there was a similar problem with an AtlasV-Cygnus launch in 2016, but the payload was going to a low-energy orbit, so the rocket happened to have enough performance margin that it didn't affect the mission. But if the payload had used the full capacity of Atlas V (like this Ariane 5 launch), it would've been a similar performance shortfall.

Bottom line: no launch vehicle is perfect, not even Ariane 5 or Atlas V. But payload can make up minor performance shortfalls.

Note: based on the actually achieved apogee and perigee and inclination, it seems that the performance shortfall may be closer to 300 to 400m/s, which would make rescue much harder, except if you used electric propulsion. Luckily, the spacecraft have electric propulsion (but JWST doesn't...).

> There is a docking ring on JWST, so it could be reboosted to a proper orbit if there's a problem with the launch.

Is the JWST designed to accommodate thrust along the axis of the docking ring?

Apply less thrust. It survived assembly, transport and launch.

Everything costs money to put into space. You don't just attach a big heavy docking ring with scotch tape. You put is somewhere that material and strength can be useful. With the safety factors involved (wouldn't want to brick a billion dollar spacecraft because you came in a few mm/sec too hot) it makes the most sense to put the docking ring somewhere structurally significant.

It's not just a matter of how much thrust... It's also the direction of the thrust relative to the center of mass of the spacecraft... (it doesn't do you any good if the thrust you apply just induces a spin)

I've always felt that when building these incredibly valuable satellites one should consider building 2. I know JWST is probably not a good example with the work required to make the mirror but but in a lot of cases one could probably replicate a rare satellite during production for much less than 2x the cost. Then you have a flight backup, and alternatively you can later double your science with another launch if everything goes smoothly on launch one.

As said probably not a reality for JWST but these high risk launches always concern me with no backup option. What a tragedy it would be.

Satellite insurance is probably cheaper (though rates may rise?)

https://en.wikipedia.org/wiki/Satellite_insurance

http://spacenews.com/space-insurers-warn-that-current-low-ra...

You can’t really insure a scientific career.

Let’s say you work on the design and implementation of a novel scientific instrument for a satellite for over ten years. That’s a job that, relatively, isn’t paid well, but if launched, the instrument will get you papers and recognition.

If the rocket launching your toy blows up, all you can get from an insurance is money, and that’s not something you value that much in life.

Some satellites also have fairly tight launch windows, for example if you want to intercept a comet.

> Let’s say you work on the design and implementation of a novel scientific instrument for a satellite for over ten years. That’s a job that, relatively, isn’t paid well, but if launched, the instrument will get you papers and recognition.

That's true, but building two of everything causes other problems. For a principal investigator (PI), they spend years drumming up support for a concept then hope that it continues to get funded, built, launched, and becomes operational. If we build 2 of everything, let's say it adds 2/3 to the cost. That means less money for other missions overall. That would make many scientists unhappy.

Government payloads are not insured. The government is "self-insured."

This happens sometimes. For example, GPS and DMSP (Defense Meteorological Satellite Program) had many blocks of identical satellites. One of the DMSP spacecraft will never launch and has been ordered to be scrapped, since it is now so out-of-date after being in storage for so long.

https://en.wikipedia.org/wiki/Defense_Meteorological_Satelli...

http://space.skyrocket.de/doc_sdat/dmsp-5d3.htm

The out-of-date aspect probably explains why this doesn't happen more. I worked on JPSS-1, a polar orbiting weather satellite. It was a follow on to NPP, but it was not an exact copy. After having experience using NPP in production (in space), naturally improvements and better technology could be integrated. These two satellite launches were separated by 6 years and a new satellite takes 4-5 years to design, build, and integrate. Think how much technology changes in 6 years.

Another instance of this:

https://en.wikipedia.org/wiki/2012_National_Reconnaissance_O...

"Hey, we've got a pair of better-than-Hubble telescopes just sitting around. Want 'em? You have to promise not to look at Earth with them, though."

Did you watch the movie Contact?

"Why build one when you can build two for twice the cost?"

So you'll often build two or three test versions of the sat that you subject to serious, and sometimes destructive, testing to simuluate launch stresses, etc. So if a given satellite blows up on the pad, they can use these test articles as a backup. So they don't really start from scratch..

Good idea. Or even just make mutiples of the rare/expensive/long-lead-time components, optimize for a second build rather than actually build two.

Better still, use a swarm of cheap unreliable satellites for the same function (often not possible)

Interestingly, James Webb's sunshield is so ridiculously big, that it could actually be used as a solar sail.

JWST is 6200kg roughly. The sunshield is about 150 square meters. Sunlight is roughly 1360W/m^2, so given Einsteins relation between momentum and energy for light: P = E/c, and increase that by a factor of 2 due to reflection (as opposed to full absorption, which would be 1), then we have 9e-6 Newtons per square meter in sunshine near 1AU, for a total of 0.00135 Newtons over the whole thing. Over 5 years, that's 36 m/s of delta-v.

That could be enough to rescue the mission due to a small performance shortfall, if you can point this carefully in the right direction.

(And 5 years is a long time, but not unheard of if you're trying to recover from a major mission failure, for instance the Japanese Venus probe which failed its 2010 Venus orbit insertion and so had to go around the sun a bunch of times and successfully inserted on the next try in 2015 using the attitude control thrusters.)

The issue, IIRC, for JWST is that it's IR optics need to be cryogenically cooled, and even in the vacuum of space that coolant will gradually boil away. Hence why JWST will have a shorter lifetime than Hubble (L2 orbit, station keeping, and serviceability notwithstanding).

JWST doesn't rely on boiling coolant. It has an on-board cryocooler.

This is "kind of good news" in that regard: It's extremely rare for the same failure to occur twice. You can't prove there are no bugs (and Ariane 5 may have been just too lucky), but you can prove to a certain extent past problems are avoided. This is why planes are so safe nowadays.

But there were two problems, not just one. 1. The communications link broke; 2. The satellite was delivered in the wrong orbit.

To clarify, the parent poster isn't affected by the gambler's fallacy; rather, they're pointing out that it's common practice for any accidents involving spacecraft to be thoroughly scrutinized to ensure that the failure mode is completely understood and can be avoided in the future.

Yes, that's exactly what I meant, thanks.

Space twitter suggests that there was no malfunction with the rocket, there was some process (read: human) failure that caused the rocket to be given the wrong instructions.

Further the satellite is going to have to burn years worth of fuel to get to where it's supposed to be.

From what I can see on the NASA website, JWST is "planning to launch between March and June 2019". I wonder if that will be delayed - I imagine they will want to track this issue down quite thoroughly and reach high confidence it won't happen again.

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