# Enola's proposal for Single Stage to Orbit **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2019, 1:36am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974 "2019-09-29T01:36:56Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 30, 2019, 12:59am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/21 "2019-09-30T00:59:45Z")
I [started a discussion thread](http://boards.straightdope.com/sdmb/showthread.php?t=882863) on the new Starship rocket. Feel free to stop by and ask questions! ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [September 30, 2019, 5:19am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/22 "2019-09-30T05:19:16Z")
The other point no one makes except maybe ftg - air. Air is only 21% oxygen. the rest is mostly nitrogen. That means you need to feed 5 times as much into the rocket engine than if carrying pure oxygen. That inert N2 must put a bit of a damper on the rocket’s performance… unless you have a magic process for separating a huge volume of gasses in real time while cooling them to cryonic temperatures. Carrying LOX instead is looking better all the time. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 30, 2019, 5:39am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/23 "2019-09-30T05:39:59Z")
> [@md2000](#): > > unless you have a magic process for separating a huge volume of gasses in real time while cooling them to cryonic temperatures. The wiki page on the [liquid air cycle engine](https://en.wikipedia.org/wiki/Liquid_air_cycle_engine) (linked above by **Enola Straight** ) says: > [@](#): > > By careful mechanical arrangement the liquid oxygen can be removed from the other parts of the air, notably water, nitrogen and carbon dioxide, at which point the liquid oxygen can be fed into the engine as usual. It’s not clear how exactly this works, though perhaps one could use the fact that oxygen will condense out of the air first. The liquid nitrogen could then be cycled back to cool the incoming air, finally exiting at the ram compression temperature, and possibly ejected out a nozzle that gives a bit of extra thrust. Still, it all seems rather difficult at the speed, size, and weight needed in an aircraft engine. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [September 30, 2019, 12:28pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/24 "2019-09-30T12:28:32Z")
> [@Dr.Strangelove](#): > > …The liquid nitrogen could then be cycled back to cool the incoming air, finally exiting at the ram compression temperature, and possibly ejected out a nozzle that gives a bit of extra thrust… The nitrogen could come in handy. Dr. Strangelove knows all this but for the OP: on almost any air-breathing SSTO you must have _active_cooling of the airframe. It must fly a “depressed trajectory” and stay within the lower atmosphere for a relatively long time while accelerating to high hypersonic speed. It like a reentering orbital vehicle but in reverse – surrounded by fiery plasma. Typically, passive thermal control systems like tiles won’t work. Regions of the vehicle skin must be lined with a network of cooling tubes. That means pumps, plumbing and possible leak issues. Any failure and you have a Columbia-like disaster, burning up in the atmosphere. A rocket engine on ascent often uses active cooling on physically small areas (vs an airframe) but in an overheat emergency it can be instantly shut down. By contrast a hypersonic airbreathing vehicle at high mach numbers requires active cooling of large regions. Any plumbing leak or issue is potentially fatal. The vehicle can’t suddenly slow down within seconds. All the weight, complexity and redundancy to implement a durable totally reliable airframe cooling system is an additional penalty that conventional launch vehicles don’t have. SSTOs are incredibly weight sensitive, and this additional burden is probably yet another reason why no airbreathing SSTO has ever been fully designed or tested even as a subscale prototype. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [October 1, 2019, 10:06pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/25 "2019-10-01T22:06:18Z")
The problem all exotic means of getting to orbit now face is that they have to beat the cost effectiveness of SpaceX’s rockets. If Starship comes even close to its stated performance, the cost to orbit will drop by at least an order of magnitude. This may be why Stratolaunch and other advanced launch concepts are dead. Even if they could be made to work, it’s going to be very hard to beat the price of a fully reusable rocket that can land back on its own launch pad. Given enough quantity of flights, SpaceX’s reusable rockets could beat a space elevator for cost of mass to orbit. The limiting factor will be demand for space launch, not anything intrinsically expansive in the mode of transportation. And the demand for space launch will go up as the cost comes down, hut we still don’t know by how much. ---
**Author:** ![Limmin](https://avatars.discourse-cdn.com/v4/letter/l/f04885/32.png) [@Limmin](https://boards.straightdope.com/u/Limmin)\ **Post date:** [October 2, 2019, 5:12pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/26 "2019-10-02T17:12:38Z")
What’s the mission, Enola? SSTO suffer from a very low ratio of payload to structural mass. For a given payload, even a 2-stage rocket has a much smaller structure + fuel mass when compared to an SSTO. I guess breathing as much air as possible from the atmosphere mitigates this issue somewhat, but maybe not that much. Hence my question. There should be a really good reason to go orbital using an SSTO, else it’s probably not worth the extra effort to develop one. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [October 2, 2019, 7:56pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/27 "2019-10-02T19:56:56Z")
> [@Limmin](#): > > What’s the mission, Enola? > > SSTO suffer from a very low ratio of payload to structural mass. For a given payload, even a 2-stage rocket has a much smaller structure + fuel mass when compared to an SSTO. I guess breathing as much air as possible from the atmosphere mitigates this issue somewhat, but maybe not that much. > > Hence my question. There should be a really good reason to go orbital using an SSTO, else it’s probably not worth the extra effort to develop one. This is the problem. The whole logic behind SSTO is that if you can reuse the whole vehicle, a smaller payload is still cheaper than a bigger payload and a throwaway rocket. But if a two-stage rocket is also reusable, then SSTO’s ONLY advantage is perhaps turnaround time on the ground, since the stacks don’t have to be reassembled. That’s a poor tradeoff for much lower performance. The minute we can reuse both stages of a two-stage rocket, SSTO as a concept is obsolete except maybe in a few niche applications. Maybe the military could use something like it - the ability to take off from a runway, get to space, do something, and fly back and land on short notice might be useful. But other than that, SSTO no longer makes sense. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [October 2, 2019, 8:30pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/28 "2019-10-02T20:30:35Z")
> [@Sam\_Stone](#): > > …The minute we can reuse both stages of a two-stage rocket, SSTO as a concept is obsolete except maybe in a few niche applications… That is true but it’s very difficult to reuse the 2nd stage. Everyday Astronaut did a whole video examining this: [https://youtu.be/4rC2Z5El-8E](https://youtu.be/4rC2Z5El-8E) ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [October 6, 2019, 2:27pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/29 "2019-10-06T14:27:36Z")
> [@TriPolar](#): > > I think some kind of rail gun like launcher would be preferred for take off. They should be able to accelerate a space plane to several times the speed of sound without the plane carrying the weight of the fuel for takeoff. [http://boards.straightdope.com/sdmb/showthread.php?t=254792&highlight=mountain](http://boards.straightdope.com/sdmb/showthread.php?t=254792&highlight=mountain) ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [October 6, 2019, 8:52pm UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/30 "2019-10-06T20:52:04Z")
> [@joema](#): > > That is true but it’s very difficult to reuse the 2nd stage. Everyday Astronaut did a whole video examining this: [https://youtu.be/4rC2Z5El-8E](https://youtu.be/4rC2Z5El-8E) You need a bigger rocket than Falcon 9 to make the second stage reusable. The SpaceX starship is fully reusable. Theoretically, one day it could fly for little more than the cost of fuel and restacking costs. Maybe 1.5 million per flight, to get 100 tonnes to orbit. Add in maintenance, insurance, and $25-50 per kilo could be possible one day with reusable rockets, if there’s ever enough launch volume to be able to fly them in large quantity. In the short term they will cost a lot more than that, but so would any other new launch technology that has to recoup R&D costs and build one-off bespoke vehicles without an assembly line. If you are thinking of a new launch technology and it can’t eventually get down in price to under $100/kg, it could be obsolete before it flies. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [October 7, 2019, 12:57am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/31 "2019-10-07T00:57:19Z")
> [@Sam\_Stone](#): > > You need a bigger rocket than Falcon 9 to make the second stage reusable. The SpaceX starship is fully reusable… By “second stage” both I and the Everyday Astronaut video meant the second booster stage, not the final payload stage. IOW the 2nd stage of a Titan II or 2nd stage of a Saturn IB, or 2nd stage of a Saturn V or 2nd stage of a Falcon 9. Traditionally the term “two stage rocket” means something like that. The 2nd stage of such a vehicle is extremely difficult to reuse. However you are right that Starship is two-stage rocket, where the reusable 2nd stage is also the payload stage. That is a different kind of two-stage rocket and except for the space shuttle I don’t think has been done before. It is very difficult to reuse those, whether the 2nd stage is simply the 2nd propulsive stage (separate from the payload stage) or the 2nd stage is a reusable vehicle which houses the payload. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [October 8, 2019, 3:01am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/32 "2019-10-08T03:01:24Z")
> [@Sam\_Stone](#): > > You need a bigger rocket than Falcon 9 to make the second stage reusable. The SpaceX starship is fully reusable. Theoretically, one day it could fly for little more than the cost of fuel and restacking costs. Maybe 1.5 million per flight, to get 100 tonnes to orbit. Add in maintenance, insurance, and $25-50 per kilo could be possible one day with reusable rockets, if there’s ever enough launch volume to be able to fly them in large quantity. > > In the short term they will cost a lot more than that, but so would any other new launch technology that has to recoup R&D costs and build one-off bespoke vehicles without an assembly line. > > If you are thinking of a new launch technology and it can’t eventually get down in price to under $100/kg, it could be obsolete before it flies. So, what would a vacation to space run me, assuming $50 a kg? Would 500 kg in payload be about the right amount? Going to need a lot of food and top quality booze during my 1 month stay in space. Plus my body (I would assume obese passengers and out of shape wouldn’t be allowed to fly due to the cramped conditions ND g forces) plus seat plus clothes plus emergency pressure suit. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [October 8, 2019, 5:01am UTC](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974/33 "2019-10-08T05:01:25Z")
Absolutely true. Plus there is training, suiting, etc. 500 kilos at $100/kilo is $50,000. Double it for healthy profit, And that’s $100k for a month in space. As a regular vacation destination, that’s within the range of anyone who has a super yacht or a Gulfstream. As a once in a lifetime bucket list vacation, it’s within range of the upper middle class. But more to the point, $100/kilo opens up space exploration to entrepreneurs, smaller science agencies, and will allow for more capable probes. A large oil company can easily invest a couple of billion in a deep sea platform. At $100/kilo, a billion dollars will lift ten million kilos into orbit. Or maybe a million kilos into lunar orbit. Or look at it another way: The Curiosity Rover weighs about 900 kilos. At $100/kilo, you could lift one into orbit for $90,000. You might be able to get it to the moon for $500,000. That opens up the possibility of the first open source, kickstarter funded space program. Also startup ventures, colleges, movie studios, industrial companies, etc. It will allow us to try many more things, which will speed up the pace of innovation. Alll we need now is some way to make money off it. A tiny detail… [Previous page](https://boards.straightdope.com/t/enolas-proposal-for-single-stage-to-orbit/840974.md?page=1)