Radian Crewed SSO Spaceplane

[daedalus1]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

[vaporcobra]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Really one of the weakest arguments out there to say that good or possible ideas "would have been done by now" in the context of spaceflight - especially post-Apollo American spaceflight, where most rockets fielded since the 70s have been shaped by shareholders, politicians, and bureaucrats as much as engineers and sound logic.

The odds are absolutely stacked against Radian but let's not try to argue that any rocket concept that hasn't been made real by 2022 is inherently a bad idea.

[daedalus1]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Really one of the weakest arguments out there to say that good or possible ideas "would have been done by now" in the context of spaceflight - especially post-Apollo American spaceflight, where most rockets fielded since the 70s have been shaped by shareholders, politicians, and bureaucrats as much as engineers and sound logic.

The odds are absolutely stacked against Radian but let's not try to argue that any rocket concept that hasn't been made real by 2022 is inherently a bad idea.

Well let's stick to the post subject.
X33 wasn't SSTO it was a technology demonstrator for Venture Star and had multiple failures and problems including cracking in the tanks. My comment is based on physics. 1 G is right on the edge of getting to orbital speed with the whole body and a significant payload unless you can scoop some oxygen from the air (Skylon).
I wish them the best of luck in this project as it would be a significant game changer.

[tea monster]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

Lockheed, Boeing and McDonnell Douglas, even Chrysler, had two-stage to orbit rocket designs that would do what Starship would do. Some of these designs go back to the 1960s. It took till now for someone to put the ideas behind those designs on a pad and try and launch it. The status quo seems to be a more powerful force than gravity for the space launch business!

[Robotbeat]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Really one of the weakest arguments out there to say that good or possible ideas "would have been done by now" in the context of spaceflight - especially post-Apollo American spaceflight, where most rockets fielded since the 70s have been shaped by shareholders, politicians, and bureaucrats as much as engineers and sound logic.

The odds are absolutely stacked against Radian but let's not try to argue that any rocket concept that hasn't been made real by 2022 is inherently a bad idea.

Well let's stick to the post subject.
X33 wasn't SSTO it was a technology demonstrator for Venture Star and had multiple failures and problems including cracking in the tanks. My comment is based on physics. 1 G is right on the edge of getting to orbital speed with the whole body and a significant payload unless you can scoop some oxygen from the air (Skylon).
I wish them the best of luck in this project as it would be a significant game changer.

Airbreathing doesn’t buy you that much. Dry mass is actually most strongly related to propellant VOLUME (and less so to propellant mass). Skylon has to carry an enormous volume of liquid hydrogen and has a high dry mass because of it.


In fact, I seem to recall HMXHMX saying that given the mass ratios skylon was proposing, it may actually be easier to make a SSTO using denser fuels without airbreathing than a SSTO using hydrogen airbreathing plus hydrolox….

…and here we are!

Dunn’s table of densified propellants for SSTO performance shows densified propylene/oxygen to be among the highest performance combinations for SSTO, beating hydrolox by a lot and even densified kerolox and methalox. Only more exotic propellants like cyclopropane improve on it, and then only slightly.

So I wonder if they’ll use something like densified propylene and oxygen. Or perhaps something like syntin (which is chemically related to cyclopropane) which the Russians/Soviets sometimes use(d).

The launch sled is a good idea, especially as it helps enable aborting the takeoff. Big brakes to stop after coming up to speed would be not viable for a SSTO vehicle without a sled. And getting it up to transonic speeds or so would be a very nice little assist as well, considering rockets burn up a lot of their propellant just to get off the pad. Rockets are least efficient at low speeds, so that small assist goes a long way.

And with the sled, they can also do captive tests of the vehicle without actually taking flight. That is easier from a regulatory standpoint (I don’t think it needs regulatory approval from the FAA), and they can even do tests before the wings are ready. They could do non-destructive qualifying tests on the airframe and propulsion systems. It’s actually a pretty good idea, to be honest. To enable the same thing without wings would mean you’d have to build a vertical launch assist tower, which would be a lot harder and more expensive.

It’s not as silly as it might seem. The launch sled buys you a lot. Using densified propellants buys you a LOT. (Although we don’t know what they’re using… if it’s hydrolox like X-33, then they will struggle. It’s one of the worst SSTO propellants to use because of its low density.)

I do hope they consider a small payload assist motor. Would make it way easier to close the design early on. Could be just a STAR motor from ATK/NG or something. Even 1-2km/s for the kick stage would help improve margins by a HUGE amount. (Although recovering the vehicle may be tough, but wings make fly back easier)

At the limit they could go with super conservative margins and just do like a big Lynx Mark III approach, launching smallsats with a sizable payload assist upper stage after getting above the Karman Line. That would be super easy to make close. They could use massive margins everywhere as it’d be basically a three stage to orbit vehicle.

[JEF_300]

powered by three liquid-fueled engines [...] At full power, this cryogenic-fueled engine will have a thrust of about 200,000 pounds.

Not Kerolox, somewhere in the range of 0.9MN per engine or ~2.7MN for the vehicle.

Last I checked, Propane was one of the dream fuels of those who were studying SSTOs. It's cryogenic, but has a density much closer to RP1 than even Methane. It's what I'd put my money on.

200,000 lbs of thrust is ~890 kN. So it's a relatively moderately sized engine, and probably manageable. And apparently, they are already test firing one! That's a pretty good sign, if it's true.

From back in 2020 (so things may have changed):

A few notable details I gleaned from a quick skim through the patent:
The Launch Sled
-Acts as a TEL, with propellant feed lines and physical supports attached to the vehicle
-Has its own engines, which fire in addition to the vehicle's engines
-May feed propellant into the vehicle to replace that burned by the vehicle's engines during the takeoff run (quick disconnect before takeoff)
-May rotate the vehicle from an initial low-drag configuration to a nose-up takeoff configuration
-Has a braking system that can bring the whole vehicle to a halt in case of emergency (the takeoff run is one long engine checkout)
-Provides some initial velocity, but more importantly, reduces the demands on (and thus mass of) the landing gear, since the vehicle is only on its gear when its tanks are empty for landing
The Vehicle
-Designed for crew and low-mass cargo, "about 5-10000 pounds to LEO" (2.3-4.5 mT), claims the F9 is overpowered for these applications
-Fuel is JET-A, oxidizer is LOX
-Main engines have a "Tripped Area Ratio"/"Tripped Flow", which changes from about 33:1 to about 60:1 in-flight, allowing good sea-level and vacuum performance (no details on how exactly this would be implemented)
-Separate set of OMS engines above the main engines, potentially pressure-fed LOX/CNG gas-gas thrusters (I know who might be developing one of those)
-In addition to the shuttle's abort modes (ATO, AOA, Downrange, and RTLS), the entire cabin can detach and perform a powered abort (picture attached), using "bipropellant thrusters" and fuel tanks in the nose, plus chutes for recovery.  Intact abort modes would require venting fuel before landing due to the low-rated gear.
-Material selection hasn't been made yet, but short-lists composites, Aluminum, Titanium, and Stainless Steel.  Heat shield material also not selected yet, but TUFROC given as example.

Too me, this is the important part.

-Main engines have a "Tripped Area Ratio"/"Tripped Flow", which changes from about 33:1 to about 60:1 in-flight, allowing good sea-level and vacuum performance (no details on how exactly this would be implemented)

It was suggested back then that this may refer to a dual bell nozzle, which seems plausible to me.

[DanClemmensen]

powered by three liquid-fueled engines [...] At full power, this cryogenic-fueled engine will have a thrust of about 200,000 pounds.

Not Kerolox, somewhere in the range of 0.9MN per engine or ~2.7MN for the vehicle.

Last I checked, Propane was one of the dream fuels of those who were studying SSTOs. It's cryogenic, but has a density much closer to RP1 than even Methane. It's what I'd put my money on.

[/quote]
Not strictly speaking cryogenic. It is a liquid at room temperature under a modest amount of pressure. You can buy LPG (essentialy liquid propane)  in any small town in the US and you can find a "propane tank" under the grill in the back yard of a lot of suburban homes. I assume you can chill to to increase the density, but I don't know that and I don't know how much it would help.

[JEF_300]

powered by three liquid-fueled engines [...] At full power, this cryogenic-fueled engine will have a thrust of about 200,000 pounds.

Not Kerolox, somewhere in the range of 0.9MN per engine or ~2.7MN for the vehicle.

Last I checked, Propane was one of the dream fuels of those who were studying SSTOs. It's cryogenic, but has a density much closer to RP1 than even Methane. It's what I'd put my money on.

Not strictly speaking cryogenic. It is a liquid at room temperature under a modest amount of pressure. You can buy LPG (essentialy liquid propane)  in any small town in the US and you can find a "propane tank" under the grill in the back yard of a lot of suburban homes. I assume you can chill to to increase the density, but I don't know that and I don't know how much it would help.

The interesting gimmick of propane as a propellant is that the range of temperatures at which it's a liquid overlaps with oxygen's, by a few degrees; in other words, at temperatures where oxygen is just barely a liquid, propane is sub-chilled to just above it's freezing point. Supposedly, you can get room-temperature RP1 densities or better out of propane by chilling it that much, and your isp will still be a little better too. Usually people are interested in the weird tank shapes that are possible when both propellants are kept at the same temperature, but for SSTOs, the interest is in that density.

[libra]

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Nonsense all the way.

[Robotbeat]

…
Material selection hasn't been made yet, but short-lists composites, Aluminum, Titanium, and Stainless Steel.
…

Lol, basically any possible aerospace structural material.

[JEF_300]

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Nonsense all the way.

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

[groundbound]

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I'm not completely disagreeing with you, but development budget and technical difficulty are not independent of each other.

[TrevorMonty]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Really one of the weakest arguments out there to say that good or possible ideas "would have been done by now" in the context of spaceflight - especially post-Apollo American spaceflight, where most rockets fielded since the 70s have been shaped by shareholders, politicians, and bureaucrats as much as engineers and sound logic.

The odds are absolutely stacked against Radian but let's not try to argue that any rocket concept that hasn't been made real by 2022 is inherently a bad idea.

Well let's stick to the post subject.
X33 wasn't SSTO it was a technology demonstrator for Venture Star and had multiple failures and problems including cracking in the tanks. My comment is based on physics. 1 G is right on the edge of getting to orbital speed with the whole body and a significant payload unless you can scoop some oxygen from the air (Skylon).
I wish them the best of luck in this project as it would be a significant game changer.

Airbreathing doesn’t buy you that much. Dry mass is actually most strongly related to propellant VOLUME (and less so to propellant mass). Skylon has to carry an enormous volume of liquid hydrogen and has a high dry mass because of it.


In fact, I seem to recall HMXHMX saying that given the mass ratios skylon was proposing, it may actually be easier to make a SSTO using denser fuels without airbreathing than a SSTO using hydrogen airbreathing plus hydrolox….

…and here we are!

Dunn’s table of densified propellants for SSTO performance shows densified propylene/oxygen to be among the highest performance combinations for SSTO, beating hydrolox by a lot and even densified kerolox and methalox. Only more exotic propellants like cyclopropane improve on it, and then only slightly.

So I wonder if they’ll use something like densified propylene and oxygen. Or perhaps something like syntin (which is chemically related to cyclopropane) which the Russians/Soviets sometimes use(d).

The launch sled is a good idea, especially as it helps enable aborting the takeoff. Big brakes to stop after coming up to speed would be not viable for a SSTO vehicle without a sled. And getting it up to transonic speeds or so would be a very nice little assist as well, considering rockets burn up a lot of their propellant just to get off the pad. Rockets are least efficient at low speeds, so that small assist goes a long way.

And with the sled, they can also do captive tests of the vehicle without actually taking flight. That is easier from a regulatory standpoint (I don’t think it needs regulatory approval from the FAA), and they can even do tests before the wings are ready. They could do non-destructive qualifying tests on the airframe and propulsion systems. It’s actually a pretty good idea, to be honest. To enable the same thing without wings would mean you’d have to build a vertical launch assist tower, which would be a lot harder and more expensive.

It’s not as silly as it might seem. The launch sled buys you a lot. Using densified propellants buys you a LOT. (Although we don’t know what they’re using… if it’s hydrolox like X-33, then they will struggle. It’s one of the worst SSTO propellants to use because of its low density.)

I do hope they consider a small payload assist motor. Would make it way easier to close the design early on. Could be just a STAR motor from ATK/NG or something. Even 1-2km/s for the kick stage would help improve margins by a HUGE amount. (Although recovering the vehicle may be tough, but wings make fly back easier)

At the limit they could go with super conservative margins and just do like a big Lynx Mark III approach, launching smallsats with a sizable payload assist upper stage after getting above the Karman Line. That would be super easy to make close. They could use massive margins everywhere as it’d be basically a three stage to orbit vehicle.

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Really one of the weakest arguments out there to say that good or possible ideas "would have been done by now" in the context of spaceflight - especially post-Apollo American spaceflight, where most rockets fielded since the 70s have been shaped by shareholders, politicians, and bureaucrats as much as engineers and sound logic.

The odds are absolutely stacked against Radian but let's not try to argue that any rocket concept that hasn't been made real by 2022 is inherently a bad idea.

Well let's stick to the post subject.
X33 wasn't SSTO it was a technology demonstrator for Venture Star and had multiple failures and problems including cracking in the tanks. My comment is based on physics. 1 G is right on the edge of getting to orbital speed with the whole body and a significant payload unless you can scoop some oxygen from the air (Skylon).
I wish them the best of luck in this project as it would be a significant game changer.

Airbreathing doesn’t buy you that much. Dry mass is actually most strongly related to propellant VOLUME (and less so to propellant mass). Skylon has to carry an enormous volume of liquid hydrogen and has a high dry mass because of it.


In fact, I seem to recall HMXHMX saying that given the mass ratios skylon was proposing, it may actually be easier to make a SSTO using denser fuels without airbreathing than a SSTO using hydrogen airbreathing plus hydrolox….

…and here we are!

Dunn’s table of densified propellants for SSTO performance shows densified propylene/oxygen to be among the highest performance combinations for SSTO, beating hydrolox by a lot and even densified kerolox and methalox. Only more exotic propellants like cyclopropane improve on it, and then only slightly.

So I wonder if they’ll use something like densified propylene and oxygen. Or perhaps something like syntin (which is chemically related to cyclopropane) which the Russians/Soviets sometimes use(d).

The launch sled is a good idea, especially as it helps enable aborting the takeoff. Big brakes to stop after coming up to speed would be not viable for a SSTO vehicle without a sled. And getting it up to transonic speeds or so would be a very nice little assist as well, considering rockets burn up a lot of their propellant just to get off the pad. Rockets are least efficient at low speeds, so that small assist goes a long way.

And with the sled, they can also do captive tests of the vehicle without actually taking flight. That is easier from a regulatory standpoint (I don’t think it needs regulatory approval from the FAA), and they can even do tests before the wings are ready. They could do non-destructive qualifying tests on the airframe and propulsion systems. It’s actually a pretty good idea, to be honest. To enable the same thing without wings would mean you’d have to build a vertical launch assist tower, which would be a lot harder and more expensive.

It’s not as silly as it might seem. The launch sled buys you a lot. Using densified propellants buys you a LOT. (Although we don’t know what they’re using… if it’s hydrolox like X-33, then they will struggle. It’s one of the worst SSTO propellants to use because of its low density.)

I do hope they consider a small payload assist motor. Would make it way easier to close the design early on. Could be just a STAR motor from ATK/NG or something. Even 1-2km/s for the kick stage would help improve margins by a HUGE amount. (Although recovering the vehicle may be tough, but wings make fly back easier)

At the limit they could go with super conservative margins and just do like a big Lynx Mark III approach, launching smallsats with a sizable payload assist upper stage after getting above the Karman Line. That would be super easy to make close. They could use massive margins everywhere as it’d be basically a three stage to orbit vehicle.

Good point about 1km/s kick stage. Something like Photon which would make all difference on rideshare missions.








Sent from my SM-G570Y using Tapatalk

[Robotbeat]

X-33, which would have delivered meaningful payload to orbit with one stage, was arbitrarily canceled by political/bureaucratic nonsense when it was practically 95% complete with every immediate problem solved. N1, a potentially great rocket, was canceled because of politics, funding, and the death of its creator. Energia and Buran, both potentially extraordinary and better than anything operating at the time, died because of funding and the collapse of the USSR. There are a thousand other paper or incomplete rockets that were never realized.

Nonsense all the way.

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I honestly disagree here. X-33 had massive. MASSIVE technical problems that were unresolved. If they hadn’t had such issues, it’s very likely it wouldn’t have faced those financial issues.

In a way, saying that they all failed due to financial issues is kinda like saying a car crash victim died because their heart stopped. Like, kinda true, but that’s only the proximate cause, not the root cause. Could’ve still shocked that dead guy’s heart and kept it limping along, but as we know from Blue Origin, sometimes no amount of money is enough to solve technical problems any faster.

[JEF_300]

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I honestly disagree here. X-33 had massive. MASSIVE technical problems that were unresolved. If they hadn’t had such issues, it’s very likely it wouldn’t have faced those financial issues.

In a way, saying that they all failed due to financial issues is kinda like saying a car crash victim died because their heart stopped. Like, kinda true, but that’s only the proximate cause, not the root cause. Could’ve still shocked that dead guy’s heart and kept it limping along, but as we know from Blue Origin, sometimes no amount of money is enough to solve technical problems any faster.

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I'm not completely disagreeing with you, but development budget and technical difficulty are not independent of each other.

I'd like to point us back to the post that started this for a moment.

If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage.

This suggests that's it is impossible - literally, technically, physically, scientifically, mathematically, etc. - impossible to build an SSTO (with meaningful payload).

We don't know that that is true, because none has ever finished.

And sure, I agree that it's extremely hard technically. And I absolutely agree that the budget issues are related to it being so technically difficult. In fact, I think it's fair to say that it may be that building an SSTO is so hard technically that it is therefore financially impossible.

But that's not the same thing as being "actually" impossible, at least in the way that term is generally used. And that is what I'm taking exception to.

I mean, if we consider things that are financially impossible to be "actually" impossible, then wouldn't it be fair to say that a crewed Mars mission is impossible. Surely, if it was at all possible to justify spending that much on such a mission, it would've happened by now? Perhaps even a return to the Moon is impossible, by this measure. Over the years, there have probably been just as many attempts to return to the Moon as SSTOs, and yet it's never panned out, for much the same reasons.


EDIT: I hate that we've dragged the thread off topic like this, but it was always gonna happen on an SSTO thread, so perhaps better to do it early.

[JEF_300]

On the actual topic of Radian's SSTO, I think it is a much more plausible proposal than most have given it credit for.

 - It uses engines of a manageable size to develop.
 - It's using a denser propellant than Hydrogen, as the SSTO experts seem to have decided is best.
 - This seems to avoid the classic SSTO trap of assuming that some wonder technology is going to magically make it all work.
 - Aerospace technology in general, and materials science in particular, has advanced dramatically since the last major attempts in the late 90s. Hopefully that means that the margins are more manageable than razor thin. Or, at least the very least are back-of-the-razorblade thin rather than edge-of-the-razorblade thin.

I'd suggest that it's a good deal more plausible a vehicle than past SSTOs, at the very least.

[Robotbeat]

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I honestly disagree here. X-33 had massive. MASSIVE technical problems that were unresolved. If they hadn’t had such issues, it’s very likely it wouldn’t have faced those financial issues.

In a way, saying that they all failed due to financial issues is kinda like saying a car crash victim died because their heart stopped. Like, kinda true, but that’s only the proximate cause, not the root cause. Could’ve still shocked that dead guy’s heart and kept it limping along, but as we know from Blue Origin, sometimes no amount of money is enough to solve technical problems any faster.

It's really not. I mean, I'm not gonna say that X-33 would've worked or anything; because really, who could know. But the fact remains that every attempt at an SSTO I am aware of was cancelled because of budget reasons rather than technical ones.

I'm not completely disagreeing with you, but development budget and technical difficulty are not independent of each other.

I'd like to point us back to the post that started this for a moment.

If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage.

This suggests that's it is impossible - literally, technically, physically, scientifically, mathematically, etc. - impossible to build an SSTO (with meaningful payload).

We don't know that that is true, because none has ever finished.

And sure, I agree that it's extremely hard technically. And I absolutely agree that the budget issues are related to it being so technically difficult. In fact, I think it's fair to say that it may be that building an SSTO is so hard technically that it is therefore financially impossible.

But that's not the same thing as being "actually" impossible, at least in the way that term is generally used. And that is what I'm taking exception to.

I mean, if we consider things that are financially impossible to be "actually" impossible, then wouldn't it be fair to say that a crewed Mars mission is impossible. Surely, if it was at all possible to justify spending that much on such a mission, it would've happened by now? Perhaps even a return to the Moon is impossible, by this measure. Over the years, there have probably been just as many attempts to return to the Moon as SSTOs, and yet it's never panned out, for much the same reasons.


EDIT: I hate that we've dragged the thread off topic like this, but it was always gonna happen on an SSTO thread, so perhaps better to do it early.

A literal reusable SSTO, HTHL or VTVL or VTHL or whathaveyou, is physically possible. I don't doubt that.

[etudiant]

On the actual topic of Radian's SSTO, I think it is a much more plausible proposal than most have given it credit for.

 - It uses engines of a manageable size to develop.
 - It's using a denser propellant than Hydrogen, as the SSTO experts seem to have decided is best.
 - This seems to avoid the classic SSTO trap of assuming that some wonder technology is going to magically make it all work.
 - Aerospace technology in general, and materials science in particular, has advanced dramatically since the last major attempts in the late 90s. Hopefully that means that the margins are more manageable than razor thin. Or, at least the very least are back-of-the-razorblade thin rather than edge-of-the-razorblade thin.
I'd suggest that it's a good deal more plausible a vehicle than past SSTOs, at the very least.

Any SSTO vehicle will need to have empty weight under 5% of the all up launch weight. That is still hugely difficult.
I'm not sure about the 'dramatic advances' in the relevant technologies. I don't know of any recent ultra light structure high performance aircraft or space vehicles, suggesting the difficult engineering challenges involved have not been addressed as yet. That said, Musk made reusable launchers happen on a shoe string budget, so perhaps there is a way.

[jongoff]

I've said this elsewhere. If this is possible it would have been done by now. You can't have any meaningful payload to orbit using one stage. Unless you resort to the very difficult method of using atmospheric oxygen in the lower atmosphere.

No, it's pretty clear to me that there are ways to make SSTOs, and even reusable SSTOs with meaningful payload.

<pedantic rant>
The physical possibility of something and its existence are two very different things. Something may be physically possible, but not worth doing. Something may also be physically possible, and worth doing, just not yet demonstrated.

For example, a powered landing VTVL first stage is something that has been theoretically possible for decades, and which many of us recognized as worth doing for decades. There were some proof-of-concept demos in the form of DC-X, Armadillo, and my old company, Masten, but it took the right combination of team, resources, and circumstances for SpaceX to finally demonstrate it in the form of a commercially operational and useful VTVL first stage. Before SpaceX had proven it, was it somehow not physically possible? Or not worthwhile? No, it just wasn't proven. There's a difference.
<end of pedantic rant>

All of that aside, while I think that SSTOs with meaningful payload are not theoretically impossible, and while I think they may be beneficial in some subset of applications, the question in Radian's case, IMO is if it's plausible that their vehicle could actually realistically work as a reusable SSTO... I'm somewhat skeptical based on the details I've heard in the past.

Though I think that a) there are things they could change to their design that could get them to a full SSTO capability, and b) even if they don't get all the way to a full "SSTO" capability, they might be able to get close enough to make something commercially useful (ie close enough that drop tanks, strapons, or a circularization motor, or in-air refueling could get them there).

~Jon

[jongoff]

(Although we don’t know what they’re using… if it’s hydrolox like X-33, then they will struggle. It’s one of the worst SSTO propellants to use because of its low density.)

I'd caveat that statement re: low density of hydrolox with "when used at normal mixture ratios in normal rocket engines". With LOX-rich TAN, you could theoretically make a stage O/F ratio of 12-18:1 work (instead of the traditional 4-6:1), which would help bulk density a ton, at the cost of lower Isp during the boost phase (which does help lower gravity losses though).

I do agree though that pure LOX/LH2 at traditional mixture ratios has crappier bulk density than you'd want for an SSTO.

When Aerojet did their TAN papers, they also looked at tri-propellant TAN -- where the main chamber was LOX/LH2, and the TAN injection was LOX/Kero. IIRC, they showed that that tripropellant approach actually closed way better than either pure LOX/Kero or pure LOX/LH2 for an SSTO designs -- high thrust and high bulk density for the start, high Isp for the end, and overall a great T/W ratio on the engines in booster mode (especially compared to typical LOX/LH2 engines).

Given that Radian hasn't publicly stated what their engines are using, it's possible they could be doing something clever/unusual like this. Though I kind of think they would've said so if they were, because that would make the whole concept seem more plausible.

~Jon