UDMH was invented because it has a much lower freezing point than regular hydrazine for exactly this reason.
A “shortcoming in the system thermal analysis performed during stage design” (for the Fregat launch vehicle’s fourth stage) was the reason two of Europe's Galileo satnav craft ended up in the wrong orbit following a launch earlier this year. As we reported back in August, two failure meant two Gallileo sats landed in the wrong …
As far as I can tell, the attitude thrusters do use UDMH, but it's hard to be sure*.
Either way, if it runs next to a liquid helium line, then basic hydrazine and UDMH will both freeze, helium is liquid at four Kelvin, UDMH will freeze anywhere below 216K.
*(there doesn't seem to be separate tanks for the attitude thrusters, so I assume they use the same fuel supply as the main engine.)
Sunday evening, I was watching Guy Martin struggling to put a wing on a Spitfire, because he'd held the bolt in his hot little hands for too long.
Liquid Helium is about a degree warmer than the cosmic background, which is still a tad frigid. I don't see any obvious reason why they're using it, but I don't design rockets. The fuel is reported as UDMH and N2O4 which is an old and well-understood combination.
What were the designers thinking?
"Liquid Helium is about a degree warmer than the cosmic background, which is still a tad frigid. I don't see any obvious reason why they're using it, but I don't design rockets"
It's used to pressurize the fuel/oxidiser tanks as they run down (amongst other things) and cryo form is used because otherwise you have to run it at insanely high pressures.
Most people aren't going to bother with the full report, but the essence is that this is an old design "flaw"(*) which was only triggered because of the longish delay between burns. Previous missions never left the upper stages idle long enough for the hydrazine to freeze and now the issue has been recognised, it won't happen again (a simple insulator will deal with it).
In any case, almost all future Gallileo launches will happen on Ariane V launchers for economy (more birds per launch). This was a test set.
(*) I put it in speechmarks because the usual short period before the upper stage is lit means than it's highly likely that thermal issues were originally considered and then put aside as not a problem.
Still unclear, putting them in the correct orbit would all their on board propellant and involve such a long sequence of changes that they would probably be obsolete by the time they were on-station.
They still provide perfectly valid positions, but it's not clear if most receivers could handle the "way out of expected range" signals you would get.
They will probably have some nominal contribution as an extra timing reference - but it looks like it's an insurance job
"They will probably have some nominal contribution as an extra timing reference - but it looks like it's an insurance job"
The constellation order was specified with 4 spare birds to account for for launch mishaps. Because so many are being built the insurance value of individual units is low (they're production line items) and there are enough spares in hand to cope with the losses.
The real issue is that this pair was intended to complete the test cluster and they can't be used for that even if their orbits are stabilised, so the end result is yet more delays before Galileo goes into production use.
Losing a 4-stack of these on an Ariane launch would be the real disaster, but the Ariane V has been extremely reliable. The ES has already been heavily used and the relightable/long coast-time EPS upper stage has already seen action, getting ATVs to the ISS. One of the big advantages of the EPS is that it can be relit for deorbiting after payload deployment, which means less space junk to contend with.
It's GLONASS system is a direct competitor to GPS and Galileo, and while Russia hasn't been hostile to Galileo like it has to GPS... well, navigation is a strategically vital field, much like oil and gas, and if I was Europe I'd not let Russia launch my navigation satellites.
I'm pretty sure prestige in the launch business is worth a lot more than possibly sabotaging a few satellites that will ultimately end up replaced anyway; this is just business as usual - which, in Rocket Science, traditionally includes plenty of fuck-ups as well...
Unlike oil and gas, Russia has no near-monopoly on launching satellites. They get chosen on price and performance history. Were their record to deteriorate to an unacceptable degree, we'd just take future launches elsewhere. (OK, there might be temporary pain because lead times are long).
I hope someone in Russia appreciates that we've exonerated them and publically admitted that this satellite failed because of an embarassing design flaw.
I also don't see how Galileo and GLONASS (and GPS) can compete. Even humble mobile phones seem able to use more than one system at the same time. It's a national security issue: our militaries want their own system, just in case the other two were both to go off-air during hostilities. (BTW, strategically, three is a stable number. Every time one player gets ahead, the weaker two will assist each other until the advantage is nullified.)
(BTW, strategically, three is a stable number. Every time one player gets ahead, the weaker two will assist each other until the advantage is nullified.)
You'll be happy to note that there are already 4 in action:
Navstar (USA), Glonass(Russia), Beidou/Compass(China, still being deployed but usable now), DORIS(France - mainly used for satellite/groundtstation positioning)
With 3 more on the way:
Gallileo(ESA), INRSS(India), QZSS(Japan),
Whilst the west may lump China and Russia together, historically there's no love lost between them and all alliances have been by necessity, not desire (China may sell the Norks Oil and Electricity for instance, but it's the Russians who created the country and keep Fatboy-un afloat)
Hypothetically, how much would I get from ESA if I was able to move these sats using a craft of my own invention (cough ground launched ionocraft/EMDrive hybrid system /cough) back to the correct orbit?
I have some ideas here for using solar energy, launching from a balloon and generating the ion field onboard thereby avoiding many if not all of the safety concerns.
Once at about 100K feet the solar powered EmDrive activates and nudges the craft into a proximity orbit intersecting the defective satellite(s) and attaches docking magnets, and over a few weeks nudges the satellite into correct orbit.
Then detaches and goes after satellite *2.
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