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Is it feasible to use either solid or bipropellant liquid rocket engines to lift off from the surface of Venus?

"Reference datum" air pressure on Venus is around 9.3 MPa; even on the top of, say, Maat Mons, the pressure would be around 5 MPa. Some modern engines have chamber pressures above 20 MPa (e.g. SSME, RD-170), so it seems possible for a rocket engine to work.

The shuttle SRBs produce substantially less pressure, around 4.3 MPa; is it practical to get a solid rocket booster up above 10MPa?

Due to the very high ambient pressure, I'd expect the expansion nozzle to be short and specific impulse to be poor. Can the performance specifications of a liquid bipropellant rocket engine optimized to exhaust into pressures from 1 to 5 MPa, using similar turbomachinery to an existing engine, be estimated? Ideally I'd like to get an estimate of the specific impulse curve of such an engine from 10 MPa to 0.1 MPa ambient.

Feel free to handwave away the thermal issues involved in maintaining liquid propellant tankage while waiting to launch from the Searing Black Calm. The goal here is to be able to simulate a rocket ascent from the surface of Venus to stable orbit, in order to answer another question on the site.

I’m well aware this is not going to be the most practical way to ascend to orbit from Venus. I’m not asking if it’s optimal or practical. Please constrain discussion to rocket engines only.

RPA crashes promptly when I ask it to compute performance at 60 bar exit pressure.

Russell Borogove
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    I looked quickly at cutting off an SSME nozzle because I had those curves...turns out that the SSME is right about 10 MPa at the throat so a stub nozzle indeed. For exit plane pressure of 1.7 MPa the specific impulse would be around ... 100. – Organic Marble Feb 22 '20 at 02:46
  • Yikes! That's gonna leave a mark on payload fraction. – Russell Borogove Feb 22 '20 at 03:46
  • Maybe the SSME is a bad choice? This is out of my wheelhouse. – Organic Marble Feb 22 '20 at 03:47
  • I mean, it's not an ideal booster engine at sea level... – Russell Borogove Feb 22 '20 at 03:49
  • @OrganicMarble The SSME is probably about as good a choice as any. Its expansion ratio is optimized for near-sea-level pressure, and that I know of, nobody has built an engine for an exit pressure much greater than sea level pressure. For sure, to operate at Venus's surface you'd have to reduce the throat diameter to drive up the chamber pressure — which will also drive up the throat temperature, pressure, and heating, so you'd better be ready to design a regenerative cooling system that carries away more heat than the SSME's. It's better to loft by balloon first, then light up at altitude. – Tom Spilker Feb 22 '20 at 04:32
  • ISTR SSME exit plane pressure matched about 50k ft but I take your point. – Organic Marble Feb 22 '20 at 04:43
  • @TomSpilker The constraints of the question I'm working toward don't allow for balloon lift; I'm willing to drive to the top of a mountain near the Venusian equator but that's it. – Russell Borogove Feb 22 '20 at 04:50
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    The structural limit on a chamber is the gauge pressure: the amount above ambient. So a chamber on Venus can still be the same pressure above ambient as on Earth. – Bob Jacobsen Feb 22 '20 at 05:08
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    @RussellBorogove Yep! From my experience at JPL, sometimes the question-askers, when they have a favorite approach in mind, pose the question in such a way as to rule out the obvious best approach. – Tom Spilker Feb 22 '20 at 05:26
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    @BobJacobsen Yes. But given a propellant chemistry, the axial temperature profile through the chamber and the throat is a function of the absolute pressures, so increasing the chamber and throat pressures will increase the down-chanber and throat temperatures. That's why I mentioned the cooling system, not the structural design. – Tom Spilker Feb 22 '20 at 05:32
  • @TomSpilker In StackExchangeSpeak that might be called the XY problem – uhoh Feb 22 '20 at 09:59
  • The existence of several organisms that use water-jet propulsion in an even denser environment shows rockets can fundamentally still work. They will indeed be greatly impaired in performance, and you will also have huge problems with atmospheric drag...you will have to keep airspeeds ~50 times lower to keep your vehicle from breaking up. It's going to be a much longer and slower climb, and that's something rockets aren't good at. You've ruled out balloon lift, what about turbojets or rotors? – Christopher James Huff Feb 22 '20 at 12:23
  • @ChristopherJamesHuff I’ve added a paragraph to clarify that non rocket solutions are out of scope for this question. There are several QAs about other strategies for Venusian ascent on the site. – Russell Borogove Feb 22 '20 at 15:21
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    I am thinking the only way this could be remotely practical is with an aerospike nozzle - I tried doubling the SSME Pc with a conventional nozzle and it was still terrible performance. I'm trying to gen up up some numbers for an "ASSME" - no spaces in the acronym please - but not sure where I will end up. – Organic Marble Feb 22 '20 at 17:26
  • Yeah, aerospike or some other altitude compensating nozzle came to mind also. For what it’s worth, the dynamic pressure constraints are pointing towards many stages of short burn time, so engines optimized for intermediate narrow pressure ranges are also potentially interesting. – Russell Borogove Feb 22 '20 at 18:11
  • just fyi the bounty here expires in about 23 hours, and there's a 24 hour grace period after that. – uhoh Feb 28 '20 at 00:24
  • @BobJacobsen The relevant quantity for the mechanical load on the chamber wall is the pressure /difference/. If you want to generate the same pressure ratios, your pressure differences will be exorbitant. – Rikki-Tikki-Tavi May 11 '20 at 00:50
  • @RussellBorogove Are combined cycle rockets allowed? E.g. a rocket engine that drives a turbine, which drives a fan, which propels the aircraft. – Rikki-Tikki-Tavi May 11 '20 at 00:52
  • @Rikki-Tikki-Tavi If you want to spec such an engine, I'll give it a shot. – Russell Borogove May 11 '20 at 01:05
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    I happen to work (remotely, from half a wold away) at one of the two non-secret labs in the world that have running combined cycle engine prototypes. When I get to see my colleagues again, I can ask them how outlandish the idea is. John Bossard is involved with the other known prototypes, maybe you can ask a question on his blog: https://plasmawind.typepad.com/ – Rikki-Tikki-Tavi May 11 '20 at 12:35

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