Radian Crewed SSO Spaceplane

[Steven Pietrobon]

Using the delta-V of multi-stage vehicles for SSTO is misleading, since the acceleration profiles are quite different compared to a SSTO. In general, the lower the Isp, the lower the delta-V required to get into orbit. This comes from a number of factors. One is that air drag deceleration is lower due to the higher vehicle mass for the same cross sectional area. Second is that maximum acceleration is reached faster due to the higher propellant mass to inert mass ratio.

For hydrolox, vacuum delta-V going into a 80x185 km orbit is about 9340 m/s, compared to 9090 m/s for kerolox, a 250 m/s saving. For RS-25, vacuum Isp is 4444 m/s, which gives a propellant mass fraction of 87.8%, however for every kg of final mass you need about 20 L of propellant, or 20 L/kg. For RD-180 with a vacuum Isp of 3325 m/s, the propellant mass fraction is 93.5%, however you only need 14 L/kg, 30% less than hydrolox! However, you do need higher thrust, and thus heavier engines due to the higher lift-off mass.

This means that for the same tank volume, hydrolox in general performs much worse than kerolox, since the final mass will be 30% less compared to kerolox!

[ncb1397]

All of which I presume Radian have been doing, although the choice of kerosene still baffles me. 

Makes sense when you consider the fuel tanks are the wings (the oxygen tank is in the main body). Integrating RP-1/kerosene/Jet-A type fuels into wings is a solved problem even for composite wings. On the other hand, programs like the X-33 had problems with the combination of complex shapes, composite materials and cryogenic fuels. Using a denser fuel also potentially gives you some more flexibility in defining the wing's shape and size. It also makes more sense from a structural stand point, kerolox has a lower fuel to oxidizer ratio, meaning more weight is in the wings where the lift is generated and less weight is in the body that has to be supported from the lift generated at the wings.

[john smith 19]

Using the delta-V of multi-stage vehicles for SSTO is misleading, since the acceleration profiles are quite different compared to a SSTO. In general, the lower the Isp, the lower the delta-V required to get into orbit. This comes from a number of factors. One is that air drag deceleration is lower due to the higher vehicle mass for the same cross sectional area. Second is that maximum acceleration is reached faster due to the higher propellant mass to inert mass ratio.

For hydrolox, vacuum delta-V going into a 80x185 km orbit is about 9340 m/s, compared to 9090 m/s for kerolox, a 250 m/s saving. For RS-25, vacuum Isp is 4444 m/s, which gives a propellant mass fraction of 87.8%, however for every kg of final mass you need about 20 L of propellant, or 20 L/kg. For RD-180 with a vacuum Isp of 3325 m/s, the propellant mass fraction is 93.5%, however you only need 14 L/kg, 30% less than hydrolox! However, you do need higher thrust, and thus heavier engines due to the higher lift-off mass.

This means that for the same tank volume, hydrolox in general performs much worse than kerolox, since the final mass will be 30% less compared to kerolox!

Interesting and I think quite counter intuitive. I'd also note that kerolox engines have achieved T/W ratio of 150:1 IIRC the best sea level hydrolox performance is roughly 59:1, so while the structural fraction is harder the the TWR is 159% better. However I am very wary of drag figures as they are very dependent on frontal area.

I don't think designing to a common volume is a common comparison method but it does raise the point that unless you go with drop tanks at some point you're going to have to wrap all that tankage in TPS and have it reenter.

I do think that due to the fundamental differences between LH2 and every other propellant in terms of density and temperature that setting the design goal as "Achieve this delta V" is basically dishonest. Set a desired orbit and let the design teams work out their own losses based on their actual vehicle. If they look abnormally low dig deeper and find out how they will achieve this low a loss figure.

[john smith 19]

To give an idea of the breadth of issues that designers have to cope with here is an old paper on some things that surfaced during shuttle testing.

A structural vibration was filtered out by the Digital Auto Pilot. But one of it's harmonics was able to get aliased back into the filters pass band. which was able to continue to excite that into a limit cycle.

The paper provides a fascinating insight into ways to test this sort of stuff and the sort of subtle ways apparently unrelated things can interact. BTW excessive vibration was a significant issue with the 2 APU's on the X-15 and caused significant programme delays.
[EDIT This suggests a useful little utility that takes a filter cutoff frequency and sampling rate maximum works out what ones above the pass band above half the sampling rate can alias back into the pass band. The key point about this story is that the cutoff filter stopped the rest of the software seeing that vibration. But IRL it didn't stop the vibration happening (which is a physical property of the structure and would be much harder to remedy if it had to be)    ]


Top tip. Watch out for resonance. Watch out for percussive vibration (more or less a square wave, so 3,5,7etc harmonics). Watch out for aliasing. Always.

[john smith 19]

One item from the RASV report was the realization from Boeing engineers that the APU's were grossly oversized for most phases of the flight.

The APU's main job was to drive the hydraulic pumps to keep the triple redundant hydraulic circuits pressurized.

However the main job of those system was TVC of the SSME's during the 10mins of ascent.  Each axis of which was estimated to use about 57hp (42Kw) of power to move. That's about 19hp per APU (full power 135hp). The power to move the aerosurfaces and lower the landing gear was considerably lower. There was also a 1hp electric pump on orbit to keep the fluid circulating and not freezing.

The Boeing engineers worked out that by fitting a power take off to the upgraded SSME (sprocket gear on the LOX turbopump?) the engines could power their own hydraulics during operation (either entirely separately or through a shared loop just between the engines in case of failure). This implies a smaller APU running at a high power level (say 80-90% of full level) and hence high efficiency, but with a smaller fuel tank (MMH IIRC)

Those design ideas are still quite viable today. They would work just as well in an electric system, with the pumps being replaced by generators or alternators driving electromechanical actuators. If the actuators allow regenerative braking (probably need to be DC) a super capacitor pack can act as the equivalent of a hydraulic accumulator, lowering the peak generating capacity needed. For mechanical simplicity the alternator/generator would be directly coupled to the APU drive turbine and the lubricant and fuel pumps electrically driven to eliminate gearing, as APU maintenance was something of a PITA.
[EDIT One last thought. You could have an option for the generator/alternator to be driven by both turbopumps, although this really would work best if they had the same operating RPM. The win would be that it could also function as a starter motor to spin up both turbines before propellant flow started. Easy enough to do  if planned into the design early enough. ]

[john smith 19]

Thanks you all for these numbers. No dogma for me, really - 6% , 7%, no problem.
Still a daunting mass fraction. Although JS19 contenair and soda can examples are interestings.

The container more than the soda can at this size. But not easy.

What was the Delta II "recipe" to get that low - "only" 1150 m/s of gravity losses ? 

This may have been better answered upthread.

With the rocket equation, even 200 m/s can make a difference... and there, we have 400 m/s variations, 8800 to 9200 m/s...

Gravity losses - such a tricky thing.

Exactly. You need to factor in the whole ascent loss budget.

I have long thought that if you want to succeed at this business you must perfect both your business model and your ascent loss model. Improving the latter can make the difference between delivering your ideal mass to your ideal orbit with an affordable LV, or having to sacrifice one or the other with the design you have, so reducing your target market.

[john smith 19]

Makes sense when you consider the fuel tanks are the wings (the oxygen tank is in the main body). Integrating RP-1/kerosene/Jet-A type fuels into wings is a solved problem even for composite wings. On the other hand, programs like the X-33 had problems with the combination of complex shapes, composite materials and cryogenic fuels. Using a denser fuel also potentially gives you some more flexibility in defining the wing's shape and size. It also makes more sense from a structural stand point, kerolox has a lower fuel to oxidizer ratio, meaning more weight is in the wings where the lift is generated and less weight is in the body that has to be supported from the lift generated at the wings.

I think it's fair to say that where fuels are concerned there is LH2 and everything else.

so Jet A buys you a standard propellant, but you could get that with LPG or LNG. But without a room temperature liquid you now need some sort of pressurization system. Those 3-5000psi tanks are rated in terms of lbs of TNT equivalent for a reason. 

Possible options here would be an autogenous system like the titan II. One interesting idea (which AFAIK has never been tried) is to use a low pressure tank of ammonia and burn that to nitrogen and water. For bonus points devise some sort of vortex combustor to separate out the water vapor  and just leave the N2 to pressurize the tank.

BTW the tanks on the D2 drone were designed with an internal pressurization of about 1psi above the outside atmospheric pressure (at 70 000ft). 

[yg1968]

Radian announces plans to build one of the holy grails of spaceflight:
https://arstechnica.com/science/2022/01/radian-announces-plans-to-build-one-of-the-holy-grails-of-spaceflight/

A Washington-state based aerospace company has exited stealth mode by announcing plans to develop one of the holy grails of spaceflight—a single-stage-to-orbit space plane. [...]

The current design of Radian One calls for taking up to five people and 5,000 pounds of cargo into orbit. The vehicle would have a down-mass capability of about 10,000 pounds and be powered by three liquid-fueled engines.

https://twitter.com/SciGuySpace/status/1483803673687953413

[yg1968]

See also this:

Radian Aerospace Emerges from Stealth, Announces Seed Funding led by Fine Structure Ventures:
https://www.prnewswire.com/news-releases/radian-aerospace-emerges-from-stealth-announces-seed-funding-led-by-fine-structure-ventures-301463373.html

https://twitter.com/thesheetztweetz/status/1483804877776171012

[DreamyPickle]

Very light on details. Apparently building their own engine but no mention of fuel? Considering X-33 background hydrogen seems likely.

taking up to five people and 5,000 pounds of cargo

Hopefully not both at once. Cargo vehicles with crew cabins are a terrible idea.

[Jim]

taking up to five people and 5,000 pounds of cargo

Hopefully not both at once. Cargo vehicles with crew cabins are a terrible idea.

No, that is not "rule".  It is cargo as in satellites and such.  Cargo for the crew is ok.

[TrevorMonty]

TSTO LV with reuseable booster is big ask for startup but SSTO is whole new level of difficulty.

Wish them the best but am very skeptical.

Sent from my SM-G570Y using Tapatalk

[lrk]

There is already a thread about them, but hasn't had any updates for over a year: https://forum.nasaspaceflight.com/index.php?topic=52422.0

Planning to use kerolox and a seemingly-complicated rocket-assisted launch sled, unless their plans have changed. 

[Robotbeat]

Bump because Radian came out of stealth.

Radian announces plans to build one of the holy grails of spaceflight:
https://arstechnica.com/science/2022/01/radian-announces-plans-to-build-one-of-the-holy-grails-of-spaceflight/

A Washington-state based aerospace company has exited stealth mode by announcing plans to develop one of the holy grails of spaceflight—a single-stage-to-orbit space plane. [...]

The current design of Radian One calls for taking up to five people and 5,000 pounds of cargo into orbit. The vehicle would have a down-mass capability of about 10,000 pounds and be powered by three liquid-fueled engines.

https://twitter.com/SciGuySpace/status/1483803673687953413

[edzieba]

While nothing closed to hard numbers, the article drops some hints that rules out some options:

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

No rocket-sled launch

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.

Space launch companies also now regularly "super chill" their liquid propellants to gain more performance during flight, which Radian plans to do.

Sub-chilled propellants.

[DreamyPickle]

While nothing closed to hard numbers, the article drops some hints that rules out some options:

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

No rocket-sled launch

Their website says "sled-assist takeoff"

[JimTheBeet]

So they're sticking to the bottom of their previous payload estimate - it still seems a little far-fetched. As has been a common theme in this thread, I guess we'll wait and see.

[Asteroza]

While nothing closed to hard numbers, the article drops some hints that rules out some options:

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

No rocket-sled launch

Their website says "sled-assist takeoff"

Jet sled then?

[Gliderflyer]

While nothing closed to hard numbers, the article drops some hints that rules out some options:

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

No rocket-sled launch

Their website says "sled-assist takeoff"

Jet sled then?

It used a rocket sled back when they were first announced in 2020:

https://twitter.com/meharris/status/1333452578663776265

[Zed_Noir]

While nothing closed to hard numbers, the article drops some hints that rules out some options:

Radian Aerospace said it is deep into the design of an airplane-like vehicle that could take off from a runway, ignite its rocket engines, spend time in orbit, and then return to Earth and land on a runway.

No rocket-sled launch

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.

Space launch companies also now regularly "super chill" their liquid propellants to gain more performance during flight, which Radian plans to do.

Sub-chilled propellants.

Seems to me that Radian might has licensed the Merlin 1D from SpaceX. A mature cryogenic engine using densified sub-chilled propellants with a 192000 lbf thrust rating at sea level.


Also some sort sled/jettisonable undercarriage will be used for the take off IMO. Since it will likely to have equipment for starting the engines and lowers the landing gears weight in spaceplane. They done something like this for Messerschmitt Me-163 Komet during WWII.