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Like the Orbiter Vehicle of the Space Shuttle was mounted on its external tank, the "gondola", the crewcar of the airship, could be likewise mounted on the last stage of the launch rocket, that would serve as the envelope of the airship.

Like with the Space Shuttle, the external tank should be connected to two solid rocket boosters that provided over 70% of the Space Shuttle's thrust. And like the Orbiter Vehicle, the gondola could have the main engines which are fueled from the external tank.

The empty weight of the Orbiter Vehicle and that of the external tank of the Space Shuttle were 78,000 kg and 26,535 kg, respectively.

Would this be achievable and would it be more economical than using a complete airship mounted on top of the launch rocket ?

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    $\begingroup$ first stages tend not to get to orbit. $\endgroup$ – JCRM Aug 10 '19 at 11:02
  • $\begingroup$ @JCRM You're right, so i've added the problem that the first stage normally would get in the way of the other ones. when not jettisoned $\endgroup$ – Cornelisinspace Aug 10 '19 at 11:20
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    $\begingroup$ I'd suspect that if we ever do airships on venus, they'd be more like Bigelow habitats - folded up during transfers, and filled with gas from storage tanks after arrival at venus. $\endgroup$ – Polygnome Aug 10 '19 at 11:28
  • $\begingroup$ @JCRM I was totally wrong with that first stage concept, so i've added the Space Shuttle example with its solid rocket boosters. $\endgroup$ – Cornelisinspace Aug 10 '19 at 16:52
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Launch vehicles don't stage to get the earlier stages out of the way, they stage to get rid of excess mass so they can actually reach orbit with a useful payload. The Shuttle ET was a bit of an exception due to various compromises in its design, and a poor design in that it hauled 27 metric tons of mass up to just short of a circular orbit that could otherwise have been used for payload.

Which brings up the next issue, propellant tanks are built to support themselves and a full load of propellant while pressurized and accelerating at multiple gravities. First stages are not built to withstand reentry from orbital velocities (since they never reach such velocities in normal operation), let alone interplanetary transfer velocities.

A first stage somehow hauled all the way to orbit and armored to survive high-velocity reentry does not have the characteristics you want for an airship envelope...it would be heavy, far heavier than a simple rigid envelope designed to operate in the atmosphere of Venus would need to be. It would still be buoyant at some altitude, but likely too deep within the atmosphere for the temperatures to be survivable for something like the lithium-aluminum Shuttle ET. (The fate of a stainless-steel Starship on Venus would be interesting to consider, but at the very least it would not perform very well as an airship.)

Realistic airships for Venus would almost certainly be non-rigid or semi-rigid, packed down to a much smaller volume and expanded after reentry.

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  • $\begingroup$ Thanks for your answer. 27 metric tons would indeed be far too heavy for a volume of 2000 kubic m. of carbon dioxide at 1 atm. By the way, i was wrong with that first stage, i meant the external tank. $\endgroup$ – Cornelisinspace Aug 10 '19 at 17:41
  • $\begingroup$ But couldn't we turn it around and use the envelope of an airship as an external tank for supplying the engines of the gondola ? $\endgroup$ – Cornelisinspace Aug 10 '19 at 17:57
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    $\begingroup$ You could, but you'd have to build those big lift cells to also contain substantial internal pressure, and the high pressure would make it more difficult to regulate buoyancy by changing the displaced volume. There'd be more surface area and seams/connections for leaks to occur at, and those leaks would threaten both buoyancy and power supply. And you'd be stuck with gaseous fuels under pressure, instead of liquid fuels. $\endgroup$ – Christopher James Huff Aug 10 '19 at 18:33

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