Wikipedia:Reference desk/Archives/Science/2021 November 30

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November 30

Rockets with solid rocket boosters launching crewed spacecraft

One of the reasons Ares I was canceled was because it was determined that launching a crewed spacecraft on a solid rocket was unsafe. Similarly, the Space Shuttle's SRBs were considered unsafe (and given that the Challenger disaster happened, those fears had basis). However, the Boeing Starliner is launched on the Atlas V in a configuration that uses solid boosters; similarly, the cancelled Hermes spaceplane was planned to be launched on the Ariane 5, which also uses solid boosters. How come launching crewed spacecraft on solid rockets or rockets with solid rockets is often considered unsafe, but this was not considered to be the case for the Atlas V launching Starliner? Is it the size of the boosters, or is it another factor? Narutolovehinata5 (talk · contributions) 00:19, 30 November 2021 (UTC)

As far as I am aware, the cancelation of Ares I had nothing to do with safety concerns of the SRBs. In fact, Ares I was seen as having a potential higher safety rating than EELV launchers, such as the Atlas V. --OuroborosCobra (talk) 00:30, 30 November 2021 (UTC)

According to this Scott Manley video, one factor for the cancellation of the Constellation program was that an Air Force study claimed that if there was a need to abort due to a problem with the rocket (i.e. an explosion), the capsule's parachutes would be burned by burning debris. Narutolovehinata5 (talk · contributions) 00:45, 30 November 2021 (UTC)

• The supposed safety rating of Ares 1 was widely mocked in the community. Aside from the parachute burning through issue mentioned above, there was also a significant issue with thrust oscillation (example link from the time), potentially subjecting the crew to significant G forces several times a second, to the point that there were serious worries about crew performance. Towards the end of the programme they were discussing madcap schemes such as upward firing thrusters to compensate.

I don't know if solid boosters are less safe: they are just way less efficient (have lower specific impulse) than liquid boosters. The Space Shuttle SRB failure resulted from notoriously ignoring signs of burn-through in the O-rings, which in turn resulted from human normalization of deviance within the contracting organization. Liquid boosters can also be throttled, turned on and off, etc., unlike solid boosters that are basically giant sparklers that can't be extinguished once lit. But if anything, liquid boosters are less reliable than solid boosters, because of the complicated turbines, pumps, cryogenics, etc. in them. Remember also the near-fatal LOX tank explosion on Apollo 13.

The US crewed spaceflight programs prior to the Shuttle all used liquid boosters, but (iirc) 1960s-70s Soviet crewed launches used supplemental solid boosters similar to what the Shuttle eventually used. I suspect this was because NASA was by then better equipped than the Soviets to surmount the hellishly difficult technical challenges of making cryogenic boosters (particularly using liquid hydrogen) reliable. 2601:648:8202:350:0:0:0:69F6 (talk) 00:34, 30 November 2021 (UTC)

As a correction, the Vostok/Voshkod/Soyuz boosters all use kerolox engines, they never used solid rockets to launch crew. Even the Buran's boosters (which were later adapted into the Zenit rocket) used kerolox, not solid propellant. Narutolovehinata5 (talk · contributions) 00:47, 30 November 2021 (UTC)

Let's not forget per-spaceflight JATO units and the shenanigans people got up to with those. See the JATO_Rocket_Car urban legend. 41.165.67.114 (talk) 06:19, 30 November 2021 (UTC)

Or the supposedly real Jet powered Volkswagen. 2601:648:8202:350:0:0:0:4F12 (talk) 08:13, 30 November 2021 (UTC)

• Also I'd like to reply here that Soviet rocket engine engineers were by no means inferior to American ones, as the IP above seems to imply. They just chose a different path. Their oxygen rich staged combustion kerosene-oxygen engines were so far ahead of what the West could do, their specs were thought to be incorrect when they were first revealed to the west after the Soviet Union went down. (See for instance the excellent "The engines that came in from the cold"). Given the general move away from hydrogen (booster) engines in new developments, one could quite easily argue they went down the right path. Fgf10 (talk) 12:44, 30 November 2021 (UTC)
  • The Soviet engineers weren't inferior by any means. They just didn't have NASA's technical infrastructure or budget at their disposal. And as Naruto mentioned, they did use liquid (kerolox) boosters as did the first stage of the Saturn V, though maybe not LH (like the Saturn V 2nd stage) which was more difficult. Anyway, in that era, quite a few important NASA engineers (such as von Braun) were German. It is likely the case, though, that the US (through Operation Paperclip) had better access to the leftover German rocketry leadership and tech, which was still relevant as late as the 1970s. 2601:648:8202:350:0:0:0:4F12 (talk)`