Author Topic: Radian Crewed SSO Spaceplane  (Read 55089 times)

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #40 on: 12/04/2020 05:47 am »
Has anyone every actually built a high speed unfixed "floating" sled before? Something that can run on salt flats or lakebeds? Say a hovercraft, or a ground effect PAR-WIG? Some old concept designs for an SSTO had a "flying" jet sled/platform that resembled a WIG.
The Thrust Super Sonic Car that broke the land speed record in the 90's could be described as such since it ran on wheels.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #41 on: 12/04/2020 05:49 am »
All of the hypersonic (and for that matter supersonic) sleds have been on tracks. The only reason they're 'sleds' on 'tracks' and not on 'rails' is because they slide on bearing surfaces rather than roll on wheels.
I was using the terms sled in the sense it's used by Boeing in the RASV papers of a powered vehicle that goes in a straight line but is not on a track, allowing (in principle) any long enough runway rated to the load to be used as a takeoff site. 
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #42 on: 12/05/2020 06:43 am »

All time record for kerolox specific impulse: must be RD-0124, 362 seconds - in vaccuum.

All time record propellant mass fraction: 0.962 - Titan 2 stage 1. Expendable, zero payload without a second stage.
Let's look at those numbers little bit more closely.
I'll use 9100m/s for orbital velocity inc losses  and 300m/s for the sled speed.

So e^((9100-300)/(9.81*362)) give a mass ratio of 12.24 or 8.17% of GTOW. If you're payload is 1% (common rule of thumb for VTO rocket SSTO) 4.5mt is 450mt vehicle with a total structural mass of 32252Kg. Payload at 2% of GTOW halves the GTOW but now you have to build the whole structure in 138764Kg.  :o

I did a quick straw pole of empty/gross weights for some combat aircraft and it came up as around 38-45%, even for ones as "sporty" as the Talon T-38, a supersonic trainer with pretty much no payload but the instructor and trainee.

The Virgin Global Challenger aircraft (an engine, air bubble and wings wrapped round a humongous fuel tank) gave a design of 17% structure, so better is possible if you sacrifice other things.

Rockets can give you 10x the T/W ratio of SoA turbofans, OTOH they also give you roughly 1/10 the Isp  :(

So can you wrap 413247Kg of propellant in 32252Kg of structural mass (including escape module) to hold 4500 of payload? that's about 2.37x better than the Virgin Global Flyer managed.

Quote from: libra
The margins are razor slim or non existing.
Agreed.

If they can then any doubts about wheather Skylon is possible (not SABRE, it's the structural fraction that's got CNES and the USAF spooked) disappear.  If they can't we will have confirmed that rocket only non LH2 HTOL SSTO (even with assistance) is (to coin a phrase) "Super damm tough" but we will have learned something about what's possible :)

Let's see what happens.
« Last Edit: 12/05/2020 07:38 am by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline ncb1397

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Re: Radian Crewed SSO Spaceplane
« Reply #43 on: 12/05/2020 06:23 pm »

I did a quick straw pole of empty/gross weights for some combat aircraft and it came up as around 38-45%, even for ones as "sporty" as the Talon T-38, a supersonic trainer with pretty much no payload but the instructor and trainee.

The Virgin Global Challenger aircraft (an engine, air bubble and wings wrapped round a humongous fuel tank) gave a design of 17% structure, so better is possible if you sacrifice other things.

Rockets can give you 10x the T/W ratio of SoA turbofans, OTOH they also give you roughly 1/10 the Isp  :(

So can you wrap 413247Kg of propellant in 32252Kg of structural mass (including escape module) to hold 4500 of payload? that's about 2.37x better than the Virgin Global Flyer managed.


Space Shuttle was about (78000 empty orbiter+26500 empty SLWT)/(78000 empty orbiter+760000 full SLWT) = 12.5%. This would have some advantages and disadvantages in terms of mass ratios.

pros
-kerolox vs hydrolox storage
-presumeably a much smaller crew compartment and payload bay relatively speaking (adds weight but not fuel capacity)
-kerolox engines can have higher thrust to weight
-maybe some advancement in material strength to weight ratios (in terms of composites vs aluminum air frames or fuel tanks)
-maybe some advancements in heat shield materials in terms of weight reduction
-3d printing
-advancements in avionics
-advancements in welding (FSW, etc.)
-advancements in computer design and analysis tools

negatives
-internal fuel tank that needs to be covered in greater amount of TPS for re-entry.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #44 on: 12/05/2020 08:32 pm »
negatives
-internal fuel tank that needs to be covered in greater amount of TPS for re-entry.
This is where it gets complicated.

That large empty fuel tank means the vehicle has a much lower ballistic coefficient.

So it hits an air density that's high enough to begin significant deceleration at a higher altitude.
Which means it can bleed off more velocity before it hits denser air and its skin temperature climbs through the roof.
Which means that it can (no guarantees it will :( ) use a lighter layer of TPS, which improves their chances of delivering a design that closes.

Trading off shape Vs volume Vs TPS is the sort of problem that's going to take lots of computer time, which fortunately has improved a great deal over the 45yrs or so since since the slab sided Shuttle was designed (as long as you don't believe all the stories CFD software tells you  ;) ).
« Last Edit: 12/05/2020 08:41 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #45 on: 12/06/2020 07:50 am »
Two years ago on another thread HMX provided a link to part of Boeing's  RASV report.

T/O speed was 220m/s (Skylon is 180m/s, which REL view as high but viable)

For anyone who wants to know what a major aerospace corp at the height of its design skills was thinking about assisted SSTO in the late 1970's it makes fascinating reading. Lots of little detail design points that anyone would need to consider.  Although some technologies are vastly better (computers, RLGs, batteries and high speed generators or alternators spring to mind)  other stuff is still as big an issue as it was then.

Figure 2 in the report reckons Wings need 38.2%, body is 28.4% and tail takes 3.6% of the dry weight of the vehicle. "Propulsion" (SSME, OMS/RCS, pressurization and prop feed system) is 18.8%

I'll leave others to work out what that implies about structural issues.

Logically there are two groups of investors for this.
a) Those who have done due diligence but are satisfied its developers have plausible ways to solve the issued raised.
b) Those who do not care.  They just want to give it a shot and see what happens.

Obviously I'm hoping most of the investors are in group a) and the promoters do have such answers.

« Last Edit: 12/06/2020 08:00 am by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #46 on: 12/06/2020 10:25 pm »
For those of youw who want to play along at home I have prepared a little game which I have called "Radian Design Game."

Usual rules apply. Blue boxes are parameters you can change. Red dots indicate notes showing known values  The rest are calculated by the game.

Since this is a game the object of the game is to keep the "Unassigned Mass" cell >0. It goes red if you don't.  Initial percentages for the tail, wings, body, landing gear and propulsion are drawn from the RASV report.

Orbital velocity is calculated from altitude and ascent losses are your choice. You can use SL Isp to set a single Isp or use a trajectory averaged Isp based on SL and Vac Isp's. You are reminded the sled speed cannot exceed the speed of light and probably should not exceed the speed of sound.
« Last Edit: 12/06/2020 10:26 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline libra

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Re: Radian Crewed SSO Spaceplane
« Reply #47 on: 12/08/2020 07:42 am »
Brilliant and interesting posts there. Couldn't remember if I had downloaded that RASV report or not, so downloaded it again.

Let me throw my 2cts into this... attached document: Dan Delong / Teledyne 1988 rocketplane, with extremely detailed mass breakdown.
Including the Space Shuttle orbiter very own mass breakdown.

Something I learned, the hard way: it is extremely difficult to find detailed mass breakdown of SSTO, TSTO, RLV, rocketplanes...
From the top of my head, the few I find
- This Delong document, for his spaceplane and the Shuttle orbiter
- some limited data for Skylon
- The RASV document linked above
- Mitchell Burnside Clapp "Black Horse" and "Black Colt" designs got detailed mass breakdowns, too
(link below)
http://www.ai.mit.edu/projects/im/magnus/bh/analog.html

Bar that... not much. Which is a little annoying.

At some point, one is left wondering "how much does a *manned RLV* cockpit weight ? and wings, and tail, and TPS, and engines, and undercarriage ?" the logical move is to try and check some historical vehicle or projects mass breakdowns... well, they are very difficult to find. The reason must be that 99% of RLV projects since 1955 remained paper-bound, nothing was build.

Quote
Figure 2 in the report reckons Wings need 38.2%, body is 28.4% and tail takes 3.6% of the dry weight of the vehicle. "Propulsion" (SSME, OMS/RCS, pressurization and prop feed system) is 18.8%

What is really crazy is that the percentages, above, are "slices" or "bits" of... 5% of the GLOW (Gross Lift Off Weight) since 95% else is the propellant in the tanks.

I created a very simple sentence to illustrate why all-rocket-SSTO are so hard...

"Takes the SSTO, standing still on the pad, ready to launch.
The propellant tanks are full.
Well - 95% of the mass must be raw propellants. Otherwise, kiss Earth orbit goodbye !
Sooo...
- the tanks around the propellants,
- and the SSTO around the tanks,
- with the payload (obviously !)

...are allocated 5%. Five percent.

And if you miss, and get 7% or even 6%, the SSTO falls short of orbit.

Put otherwise...

I'm the proud owner of a Fiat Grande Punto since 2011. A very nice car. It weights 1000 kg. And since the tank hold 45 L of gasoline, that must be 40 kg in mass.  40 kg out of 1000 kg. Leaves plenty of margin.

Now If I applied "all-rocket SSTO" numbers to it... the gasoline in the tank would represents 950 kg. No kidding.

This mean that
a) the tank around the gasoline,
b) the car around the tank,
c) and the payload in the car (myself, my kid, my wife, the dog and the furniture)
would have to fold into 50 kg.

Because, if the car busted the 1000 kg limit, it wouldn't work anymore. It would't move.

Would you buy such a car ? I wouldn't, because AFAIK, I'm (to my regret) much more than 50 kg in weight, all by myself...

GAME OVER. YOU LOSE.
« Last Edit: 12/08/2020 08:07 am by libra »

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #48 on: 12/08/2020 08:40 pm »
What is really crazy is that the percentages, above, are "slices" or "bits" of... 5% of the GLOW (Gross Lift Off Weight) since 95% else is the propellant in the tanks.
That is what makes this so very tricky to get to work.  :(

Quote from: libra
I'm the proud owner of a Fiat Grande Punto since 2011. A very nice car. It weights 1000 kg. And since the tank hold 45 L of gasoline, that must be 40 kg in mass.  40 kg out of 1000 kg. Leaves plenty of margin.

Now If I applied "all-rocket SSTO" numbers to it... the gasoline in the tank would represents 950 kg. No kidding.
Actually it's somewhat worse than that.   :(
As a hydrocarbon rocket you'll carry about 2.6x that mass of LO2 as well.

Which makes the absolute mass of your 5% bigger but the volume you have to wrap bigger as well. Your car is an air breather, which makes it considerably easier to support. If only you could use that insight....

Fortunately all is not entirely lost....

Consider a 20 foot shipping container mfg in composites like this  It weighs 3450lb and holds 49460lbs, a structural fraction of 6.52%. It is expected to survive with a stack weight of423,238 lbs on top of it (IE about a 8 stack high) with an expected life of 20-30 years. 

Or the classic humble soda can. In metric countries this holds 330ml of fluid (which we know is 95-99% water so about 330g. It's empty mass is about 11g IE 3.225% of payload. BTW I have stacked 10 unpressurized (but water loaded) soda cans on top of each other without collapse. Although they are pressurized to about 3bar the can is not a pressure stabilized tank like the Atlas 1's, 2's and Centaur tanks.

These improvements have been driven solely by the economics of shipping. With enough 10ths of a gram saved (or kilos) off each unit that adds additional carrying capacity to the vehicle.

Better is possible.

An interesting challenge in the game is what you have to do if you use the usual SL and Vac Isp's of a Merlin for the stage.  What else has to accommodate to allow that?


MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #49 on: 12/08/2020 09:48 pm »
Brilliant and interesting posts there. Couldn't remember if I had downloaded that RASV report or not, so downloaded it again.
Thank you.

Another idea which should be on any SSTO (or assisted SSTO) is sub cooling of propellants.
Attached is a report on the LOX sub cooler for the Taurus II ELV. Note that with just regular NBP LN2 the resistance between the LN2 and the LOX is 0.9K, which is pretty impressive.  And still leaves the flash boiled GN2 cold enough to freeze most hydrocarbon fuels rock solid (without careful control of relative flow rates).
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline ncb1397

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Re: Radian Crewed SSO Spaceplane
« Reply #50 on: 12/08/2020 10:52 pm »

"Takes the SSTO, standing still on the pad, ready to launch.
The propellant tanks are full.
Well - 95% of the mass must be raw propellants. Otherwise, kiss Earth orbit goodbye !
Sooo...
- the tanks around the propellants,
- and the SSTO around the tanks,
- with the payload (obviously !)

...are allocated 5%. Five percent.

And if you miss, and get 7% or even 6%, the SSTO falls short of orbit.


That isn't necessarily true.  I graphed both 9000 m/s and 9300 m/s and as long as you can get average ISP of around ~330, dry mass around ~6% is sufficient if 9300 m/s is requires and ~7% is sufficient if 9000 m/s is required. Merlin 1D sea level performance is 282 seconds and vacuum performance is 311, but the vacuum variant gets about 348. RD-180 is between 311(sea level) and 338 (vacuum), so getting 330 average shouldn't be impossible. Even at 320, you still can go to 5.5-6% (of course, lower is better).

edit: average isp isn't really the best way to describe the above. Two systems that have the same average isp might perform somewhat differently from a change in velocity perspective. But starting at the RD-180 sea level isp of 311 and linearly moving to 338 over the burn, a vehicle that is 6% dry weight and 94% propellant gets about 9100 m/s. Which, adding 300 mph or 135 m/s for the rocket sled, could probably get you to orbit (dependent on gravity/drag loses and latitude).

« Last Edit: 12/09/2020 01:52 am by ncb1397 »

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #51 on: 12/09/2020 06:16 am »
That isn't necessarily true.  I graphed both 9000 m/s and 9300 m/s and as long as you can get average ISP of around ~330, dry mass around ~6% is sufficient if 9300 m/s is requires and ~7% is sufficient if 9000 m/s is required. Merlin 1D sea level performance is 282 seconds and vacuum performance is 311, but the vacuum variant gets about 348. RD-180 is between 311(sea level) and 338 (vacuum), so getting 330 average shouldn't be impossible. Even at 320, you still can go to 5.5-6% (of course, lower is better).
Quite true. But while average Isp of 330secs seems quite reasonable I'd say it's actually pretty hard. IIRC Merlin runs SL Isp of 311 and Vac Isp of 326.
Quote from: ncb1397
edit: average isp isn't really the best way to describe the above. Two systems that have the same average isp might perform somewhat differently from a change in velocity perspective. But starting at the RD-180 sea level isp of 311 and linearly moving to 338 over the burn, a vehicle that is 6% dry weight and 94% propellant gets about 9100 m/s. Which, adding 300 mph or 135 m/s for the rocket sled, could probably get you to orbit (dependent on gravity/drag loses and latitude).
Ascent losses can make a huge difference to the viability and capability of a launch vehicle.
Note the range of total delta V's to achieve orbit. It's over the SL speed of sound.

 While it can be argued that like-for-like comparison is difficult this does show that single numbers are a very broad brush approach and detailed ascent loss modelling is essential. HTO means you're already moving in the right direction from the moment of take off.

One quite subtle change that has been happening since the 70's is the way the ability to track detailed information about every single part of a design has improved. The recognition that a lot of the data that's used in mfg will have to be retained (in aerospace) throughout the whole life cycle of the vehicle and the ease with which that can be done.

In contrast the Shuttle programme failed to do this and a Boeing study found there were more than a 100 separate databases (some paper based) being maintained by different parts of the various organizations responsible.  :(

In particular the ability to have parts property changes cascade down through other parts (or even to just raise an alarm when a key property like a parts mass or moment of inertia has changed). Likewise when a part needs replacing on the operational vehicle that should trigger the whole supply chain from checking a new one out of stores to triggering re-supply or a new mfg order.

While it sounds very dull  :) I've come to realize that effective data management on complex projects of all data (not just the stuff on computers) is a critical enabling factor in the success or failure of complex (not necessarily big) projects.
« Last Edit: 12/09/2020 06:25 am by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline libra

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Re: Radian Crewed SSO Spaceplane
« Reply #52 on: 12/09/2020 03:10 pm »
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.


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

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.

Offline lrk

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Re: Radian Crewed SSO Spaceplane
« Reply #53 on: 12/09/2020 03:33 pm »
What was the Delta II "recipe" to get that low - "only" 1150 m/s of gravity losses ?  :o

Super high TWR early in flight, with lots of SRBs (including air-lit ones in some configurations.)

Having wings (even with a mediocre TWR) should actually help gravity losses significantly as the lift offsets gravity early in flight when losses would otherwise be the highest.  Recall that the wings on the Pegasus rocket actually increased the payload capacity, despite the added mass. 

Offline Craftyatom

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Re: Radian Crewed SSO Spaceplane
« Reply #54 on: 12/09/2020 05:18 pm »
What was the Delta II "recipe" to get that low - "only" 1150 m/s of gravity losses ?  :o

Super high TWR early in flight, with lots of SRBs (including air-lit ones in some configurations.)

Having wings (even with a mediocre TWR) should actually help gravity losses significantly as the lift offsets gravity early in flight when losses would otherwise be the highest.  Recall that the wings on the Pegasus rocket actually increased the payload capacity, despite the added mass.
Interesting - I always tend to think of wings in terms of drag, but of course there's an L/D ratio for a reason.  Not sure how much Pegasus' math changed due to being launched in thinner atmosphere (and the extra pitch-up it provided prior to ignition), but it does at least suggest that trades are needed before we can tell anything with certainty.
All aboard the HSF hype train!  Choo Choo!

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #55 on: 12/09/2020 08:46 pm »
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.


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

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.
You'll note that it has the 2nd highest drag losses of the vehicles, suggesting it spends an extended amount of time in the atmosphere, but its steering losses are very low.

IOW it prioritizes moving toward the horizontal direction over getting out of the majority of the atmosphere as quickly as possible. The "9" in its type number indicates it had 9 SRB's. This type fired in 2 groups, 6 at launch, increasing takeoff acceleration, and 3 (with altitude optimized nozzles) after the first 6 burnt out but before 1st stage MECO. So the design could be viewed as a 2 1/2 stage rather than a 2 stage vehicle. That 2nd burst of thrust happens when the stage is quite light so while the absolute thrust is lower the acceleration it contributes is likely higher.

The combination of higher acceleration and early start (giving low steering losses as the nozzle is only slightly off the axis of the line of the vehicle) to going horizontal are probably the main reasons for the low overall losses.

Fortunately what used to take hours of computer time can now be run in seconds. At this level every  belief, rule of thumb and old wives tale (of which this industry is somewhat prone) needs to be examined
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #56 on: 12/09/2020 08:54 pm »
Super high TWR early in flight, with lots of SRBs (including air-lit ones in some configurations.)

Having wings (even with a mediocre TWR) should actually help gravity losses significantly as the lift offsets gravity early in flight when losses would otherwise be the highest.  Recall that the wings on the Pegasus rocket actually increased the payload capacity, despite the added mass.
The lead developer for Pegasus answered questions on the development process on the Pegasus thread some
years back. I recall coming across an old Pop Sci article written around the time the original version first launched
which also talked about their approach

Orbital was strapped for cash at the time. They'd gone in big developing the Inertial Upper Stage for the Shuttle then Challenger happened so were looking for a new project to use their rocket knowledge and get some cash in. 

IOW they wouldn't have added wings to the design unless it gave substantial benefits to justify having them made. Keep in mind the wing has no propellant storage or control surfaces (fins on the rear of the first stage provide those).
« Last Edit: 12/09/2020 08:55 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #57 on: 12/09/2020 09:37 pm »
The questions I am curious to ask anyone who downloaded my game is

Did you get a configuration that got to the orbit you chose?

If you did what assumptions did you have to make or change to do so?

AFAIK the Merlin Isps are 311/326secs. When I used those for the engine parameters I found I had to cut overall losses by about 300m/s and lower the landing gear mass to the 2.8% of dry mass which Boeing thought possible in the advanced version of the RASV design.
The landing gear of both the XB70 and the B58 were lower than this so I expected it to be viable.
Water cooling, with the unused water dumped overboard just after launch, is another viable option to lower landing gear mass further (SOP in the 18 wheel truck cab racing fraternity).

I don't have a good enough feel for the mass drivers for body and wing masses to know how conservative (or not) the structures were.  I do know 2 things.
1) From roughly the 50's to the 70's a lot of work was done on alternative designs (and materials) for wing and body stiffeners, their placement and sizing. The goals were to lower mfg cost and/or mass per unit area to give higher performance or higher profits. A fair sized chunk of that has been around "space planes" (Boeing was prime for the  X-20) or M5+ designs, so high temperature issues were part of those architectures, along with TPS considerations. Nothing ever flew, but some of it got tested in high speed, high temperature wind tunnels. Lots of possible approaches.

2) Boeing approached the USAF to offer RASV as a fixed price contract. This AFAIK was unique from a major aerospace prime for a FOAK vehicle without an extensive established market and suggests
a) The Boeing Board wanted the business so much they'd swallow any cost overruns
b) They were so confident of their design teams ability to deliver what they said they could at the cost they predicted that they weren't worried about cost overruns to begin with.

Given the Board were that serious about wanting the contract my instinct is the structures were in the tough-but-viable range rather than the cat-in-hells-chance of being achievable. Avoiding the extreme cryogenic engineering of LH2 should improve the viability. Time will tell if this design can take the performance hit on using kerosene.
« Last Edit: 12/09/2020 09:39 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline ncb1397

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Re: Radian Crewed SSO Spaceplane
« Reply #58 on: 12/09/2020 09:40 pm »
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.


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

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.
You'll note that it has the 2nd highest drag losses of the vehicles, suggesting it spends an extended amount of time in the atmosphere, but its steering losses are very low.


given the displacement formula

s= ut + (1/2)a*t*t

u or initial velocity is zero for a VTO rocket and a * t is velocity. So, we can simplify to s= (1/2) *v * t or v = 2s/t with s being displacement (in this case the altitude of the rocket). So, we know that for a certain altitude, the velocity for a linearly accelerating vehicle is inverse to the time it takes to get there (half the time, double the velocity). We also know that drag scales to the square of the velocity, so if you half the time, you are actually increasing the instantaneous drag at a certain altitude by 4x. Total drag would be average drag * time over the course of flight, so halving time as a result of increasing thrust isn't going to be enough to overcome 4x the instantaneous drag as a result of halving the amount of time. So, there is a trade off somewhat between aerodynamic losses and gravity losses. Your aerodynamic losses will increase if you increase your thrust as gravity losses decrease. This explains why the low gravity loses are correlated with higher aerodynamic losses. But the higher aerodynamic losses isn't associated with more time in the atmosphere, the higher thrust rocket spends less time in the atmosphere.

At least, that is what I could come up with. Feel free to point out any logical/math/physics errors.
« Last Edit: 12/09/2020 09:46 pm by ncb1397 »

Offline john smith 19

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Re: Radian Crewed SSO Spaceplane
« Reply #59 on: 12/10/2020 06:31 am »

given the displacement formula

s= ut + (1/2)a*t*t

u or initial velocity is zero for a VTO rocket and a * t is velocity. So, we can simplify to s= (1/2) *v * t or v = 2s/t with s being displacement (in this case the altitude of the rocket). So, we know that for a certain altitude, the velocity for a linearly accelerating vehicle is inverse to the time it takes to get there (half the time, double the velocity). We also know that drag scales to the square of the velocity, so if you half the time, you are actually increasing the instantaneous drag at a certain altitude by 4x. Total drag would be average drag * time over the course of flight, so halving time as a result of increasing thrust isn't going to be enough to overcome 4x the instantaneous drag as a result of halving the amount of time. So, there is a trade off somewhat between aerodynamic losses and gravity losses. Your aerodynamic losses will increase if you increase your thrust as gravity losses decrease. This explains why the low gravity loses are correlated with higher aerodynamic losses. But the higher aerodynamic losses isn't associated with more time in the atmosphere, the higher thrust rocket spends less time in the atmosphere.

At least, that is what I could come up with. Feel free to point out any logical/math/physics errors.
It's not quite that simple.  Gravity losses are the resolved vertical component of thrust.If you measure the angle of the rocket from vertical then they are the Cos X component, if you measure from horizontal the Sin X component of thrust.  It is proportional to time of thrust.

Drag is proportional to the square of the cross sectional area of the vehicle and the velocity.

The key thing to note is the relative magnitudes of losses. Gravity losses are in the 1000m/s+ range, Drag losses in the 10s of m/s. Something that halves gravity losses and doubles drag losses is a huge win in terms of the total delta V the vehicle has to provide.

At this point  you need to start factoring in all sorts of things. How atmospheric density varies with altitude. How mixture ratio changes relative tank sizes and hence total volume that needs to be encloses. Aspect ratio of tanks. Volume reduction if you do sub cooling. And so on.

Now you're off simple calculations and into modelling instead.

All of which I presume Radian have been doing, although the choice of kerosene still baffles me.  :(
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

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