SSTO challenge

[tnphysics]

No, I was referring to the aforementioned nuclear lightbulb concept.

[KelvinZero]

Ah sorry tnphysics, that was sort of an in joke with Hop.

More on topic, with the limitations imposed I think I would still put beamed power propulsion well ahead of nuclear launch rockets. I mean beamed can still mean nuclear, but on the ground behind several meters of concrete and a few hundred miles from the launch site.

However I dont think there should be yet another beamed power propulsion thread that is not sensibly named beamed power propulsion.

[Patchouli]

I think a descent SSTO could be obtained using an aero spike based off SSME hardware or a SSME with hydrocarbon TAN.
Maybe go with four RL-10s as sustainers/landing engines.
Another option the RD-701 engine from MAKS-OS but with a plug nozzle.

The size range for a cheap demonstrator I don't think anything smaller then Bono's SASSTO will have a practical payload let alone work unless something else takes it above most of the atmosphere.

But SSTOs seem to work best if you make them gigantic like NEXUS as the law of cubes works in your favour.

BTW would dropping the SSME or RD-701 in stage and a half configuration  after 75% of the propellant has been expended and using the RL-10s be cheating?
Also the RL-10s would loose the RCC bell extensions during reentry so they'll have the right ratio for atmospheric use.

[tnphysics]

Yes it would be cheating.

Why? The idea is for the vehicle to land, refuel, and launch with at most a hour or two of maintenance- by a small crew- between flights. This prohibits any ground assembly.

Also-use LOX/LCH₄, NOT LOX/LH₂. The first gives higher payload capacity, as well as much simplified handling. I would recommend a LOX-rich staged combustion cycle, as LCH₄ rich staged combustion would cause coking in the preburner.

Maybe a modified NK-33? Could it be modified to handle the methane fuel?

Also, what about commercial LNG? It is cheaper, and the intent is to reduce operating costs to such an extent that fuel is a significant expense.

[mlorrey]

Yes it would be cheating.

Why? The idea is for the vehicle to land, refuel, and launch with at most a hour or two of maintenance- by a small crew- between flights. This prohibits any ground assembly.

Also-use LOX/LCH₄, NOT LOX/LH₂. The first gives higher payload capacity, as well as much simplified handling. I would recommend a LOX-rich staged combustion cycle, as LCH₄ rich staged combustion would cause coking in the preburner.

Maybe a modified NK-33? Could it be modified to handle the methane fuel?

Also, what about commercial LNG? It is cheaper, and the intent is to reduce operating costs to such an extent that fuel is a significant expense.

Ah I see you build your launchers out of handwavium.

Until you can build structural components out of smoke and toothpicks, a TPS out of goosedown and cotton candy, and fuel tanks out of ziplock baggy material, you'll never reach the mass fractions required to be an SSTO RLV using chemical fuels UNLESS you use air breathing systems.

SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

[Robotbeat]

...
SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

What about balloon tanks? Why not those?

[tnphysics]

Yes it would be cheating.

Why? The idea is for the vehicle to land, refuel, and launch with at most a hour or two of maintenance- by a small crew- between flights. This prohibits any ground assembly.

Also-use LOX/LCH₄, NOT LOX/LH₂. The first gives higher payload capacity, as well as much simplified handling. I would recommend a LOX-rich staged combustion cycle, as LCH₄ rich staged combustion would cause coking in the preburner.

Maybe a modified NK-33? Could it be modified to handle the methane fuel?

Also, what about commercial LNG? It is cheaper, and the intent is to reduce operating costs to such an extent that fuel is a significant expense.

Ah I see you build your launchers out of handwavium.

Until you can build structural components out of smoke and toothpicks, a TPS out of goosedown and cotton candy, and fuel tanks out of ziplock baggy material, you'll never reach the mass fractions required to be an SSTO RLV using chemical fuels UNLESS you use air breathing systems.

SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

Well, the WBC has a large enough mass ratio for expendable, and I suspect that reuse does not require doubling the mass (It could be SSTO even then). Also, if you use a plug nozzle as your heat shield, then could not a parachute be used for landing?

[mlorrey]

Yes it would be cheating.

Why? The idea is for the vehicle to land, refuel, and launch with at most a hour or two of maintenance- by a small crew- between flights. This prohibits any ground assembly.

Also-use LOX/LCH₄, NOT LOX/LH₂. The first gives higher payload capacity, as well as much simplified handling. I would recommend a LOX-rich staged combustion cycle, as LCH₄ rich staged combustion would cause coking in the preburner.

Maybe a modified NK-33? Could it be modified to handle the methane fuel?

Also, what about commercial LNG? It is cheaper, and the intent is to reduce operating costs to such an extent that fuel is a significant expense.

Ah I see you build your launchers out of handwavium.

Until you can build structural components out of smoke and toothpicks, a TPS out of goosedown and cotton candy, and fuel tanks out of ziplock baggy material, you'll never reach the mass fractions required to be an SSTO RLV using chemical fuels UNLESS you use air breathing systems.

SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

Well, the WBC has a large enough mass ratio for expendable, and I suspect that reuse does not require doubling the mass (It could be SSTO even then). Also, if you use a plug nozzle as your heat shield, then could not a parachute be used for landing?

WBC?

[mlorrey]

...
SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

What about balloon tanks? Why not those?

Balloon tanks (aka like Atlas original design) must remain pressurized to maintain structural strength, but also really aren't that great at dealing with non-axial loads. I highly suspect that the uneven heating that is inevitable with even a butt-first reentry with a shield on an aerospike base plug, will cause a balloon tank to buckle.

[tnphysics]

Yes it would be cheating.

Why? The idea is for the vehicle to land, refuel, and launch with at most a hour or two of maintenance- by a small crew- between flights. This prohibits any ground assembly.

Also-use LOX/LCH₄, NOT LOX/LH₂. The first gives higher payload capacity, as well as much simplified handling. I would recommend a LOX-rich staged combustion cycle, as LCH₄ rich staged combustion would cause coking in the preburner.

Maybe a modified NK-33? Could it be modified to handle the methane fuel?

Also, what about commercial LNG? It is cheaper, and the intent is to reduce operating costs to such an extent that fuel is a significant expense.

Ah I see you build your launchers out of handwavium.

Until you can build structural components out of smoke and toothpicks, a TPS out of goosedown and cotton candy, and fuel tanks out of ziplock baggy material, you'll never reach the mass fractions required to be an SSTO RLV using chemical fuels UNLESS you use air breathing systems.

SSTO RLV requires an flight average Isp of 600 seconds using standard aerospace construction methods and materials.

Well, the WBC has a large enough mass ratio for expendable, and I suspect that reuse does not require doubling the mass (It could be SSTO even then). Also, if you use a plug nozzle as your heat shield, then could not a parachute be used for landing?

WBC?

Wide Body Centaur

Proposed Atlas V upgrade

Propellant Mass Fraction .94 with LH₂/LOX

[Arthur]

Here is a challenge: Design a concept (BOTE) for an SSTO RLV. It must be capable of high flight rates (several times per day). Market is space tourism. An NTR is allowed, but air-launch is not.

Assuming a mere one flight per week (with 2 weeks off) and a modest capacity of 10 passengers, and an ‘affordable’ ticket price of $1 million per seat … is there a market for 500 passengers to LEO per year?
Will the demand still be there if the cost is closer to the $30 million for a Russian seat to ISS?

If not, then I would question the need for any RLV (SSTO or TSTO).
IM(very)HO, we are not even close to the point where the launch rate makes RLVs more economical than ELVs.

Some VERY rough numbers to guess-timate a demand curve:
At $20-30 million per flight, Russia has sold an average of 1 seat per year.
At $200,000 per sub-orbital flight, Virgin Galactic has 300 pre-orders.
At $1-3 million per flight, I would guess a demand closer to 10 passengers per year or about 1 flight per month at 1 pilot and 1 passenger per flight. I think that you may have trouble making ends meet on a SSTO RLV.

[jongoff]

Here is a challenge: Design a concept (BOTE) for an SSTO RLV. It must be capable of high flight rates (several times per day). Market is space tourism. An NTR is allowed, but air-launch is not.

Assuming a mere one flight per week (with 2 weeks off) and a modest capacity of 10 passengers, and an ‘affordable’ ticket price of $1 million per seat … is there a market for 500 passengers to LEO per year?
Will the demand still be there if the cost is closer to the $30 million for a Russian seat to ISS?

If not, then I would question the need for any RLV (SSTO or TSTO).
IM(very)HO, we are not even close to the point where the launch rate makes RLVs more economical than ELVs.

Some VERY rough numbers to guess-timate a demand curve:
At $20-30 million per flight, Russia has sold an average of 1 seat per year.
At $200,000 per sub-orbital flight, Virgin Galactic has 300 pre-orders.
At $1-3 million per flight, I would guess a demand closer to 10 passengers per year or about 1 flight per month at 1 pilot and 1 passenger per flight. I think that you may have trouble making ends meet on a SSTO RLV.

Arthur,
There have been studies on this topic you might want to peruse...

On a serious note though, yeah at $1M per seat price you're not going to get enough demand to justify a fleet of 10 passenger RLVs.  You really need to get the price down into the $100-500k range to get anywhere close to that level of demand...  But why do you need to go for that big of an RLV at first?  Why not a 2 or at most 3-seater (one pilot and 1-2 passengers)?  At $1M per seat, I could see enough demand per year just for orbital tourism flights to justify one or two companies with 1-2 passenger RLVs.  But there are other markets that are also interesting--not all passengers have to be tourists.  While right now most astronauts are government employees being flown on rockets done by their own country, if the price was cheap enough, you might see a lot more...what does Bigelow call them..."sovereign clients" flying into space.  Also, if the access is *frequent* and *dependable*, I think you can actually start to see useful commercial microgravity research.

So long as you don't arbitrarily assume way too big of an RLV to start with, I think the market is there.  The problem is that to-date, most RLV studies by AF and NASA have assumed you want to use the RLV for everything, and focused entirely on existing markets, which tends to drive up the minimum size by a huge amount compared to what I think the first commercial orbital RLVs will likely do.  I could very well be wrong, but I think I've got better than even odds of being right when I guess that the first commercially successful orbital RLVs will have payloads less than 1000lb.

~Jon

[Arthur]

The opening post suggested multiple flights per day. At 2 flights per day and 1 passenger per flight and 5 days per week, that works out to 10 passengers per week. But that requires 10 launches and 20 people to orbit every week just to provide 10 commercial seats per week.

Assuming that each additional seat has a lower marginal cost, I simply combined the commercial seats into 1 launch per week of 1 pilot and 10 passengers. I assumed that 11 people to orbit would be cheaper than 20 people to orbit (for the same total revenue).

Both plans require a demand of 10 passengers per week (500 passengers per year) which I have concerns is an unrealistic demand for any remotely possible price for a SSTO RLV.

Assuming a $500,000 per seat price will net 500 passengers per year, the 2 seat RLV will need a per launch cost less than $500,000 (500 launches per year) and the 11 seat RLV will need a per launch cost less than $5,000,000 (50 launches per year).

Good Luck.

[jongoff]

The opening post suggested multiple flights per day. At 2 flights per day and 1 passenger per flight and 5 days per week, that works out to 10 passengers per week. But that requires 10 launches and 20 people to orbit every week just to provide 10 commercial seats per week.

I forgot that's where the conversation started.  Yeah, that's challenging for a first generation RLV of any sort.

Both plans require a demand of 10 passengers per week (500 passengers per year) which I have concerns is an unrealistic demand for any remotely possible price for a SSTO RLV.

Oh, I don't think 500 passengers per year is unrealistic at all:

1-for a 2nd or 3rd generation commercial RLV'
2-after the market has had time to grow substantially

Assuming a $500,000 per seat price will net 500 passengers per year, the 2 seat RLV will need a per launch cost less than $500,000 (500 launches per year) and the 11 seat RLV will need a per launch cost less than $5,000,000 (50 launches per year).

I think it's quite possible to meet those kind of launch prices.  Just not right away.  All that said, I don't think people are a good first market for RLVs.  You want to amortize the first generation development over markets that are both bigger, and less demanding.  I think propellants are likely closer to the killer app for getting the door open.

As to whether you're talking SSTO or TSTO RLVs, I'm more agnostic on that.

~Jon

[kkattula]

The opening post was 'unrealistic'.

How many orbital destinations can be reached, and returned from, several times per day? Only equatorial orbits from equatorial launch sites. Space tourists will want to see their own country and town etc. Most of those won't be visible from equatorial LEO.

At best space tourism would launch alternate vehicles once per day to a single destination. With multiple destinations, and multiple launch/landing sites, it might be possible for a vehicle to launch from one and land at another, once per day, but that's about the best you would get.

Realistically, an RLV with a turn around of 2 to 8 days is probably more than enough. Providing it doesn't take thousands of people to service it during that period!

[93143]

Skylon?

Seconded.

I know it's bad for an engineer to get on a bandwagon and stop thinking, but sometimes I'm amazed at how much effort it takes to get people to even acknowledge the Skylon concept's existence in an SSTO thread...

It's supposed to have a 48-hour turnaround time, which doesn't technically meet the requirements in the OP, but as pointed out this requirement is probably overly stringent given the likely average mission length.

The plan is for Skylon to have a Passenger & Logistics Module that functions as an ordinary payload, requiring no modifications to the actual spaceplane.  It could potentially take 30 or 40 people to orbit.  As their new video notes, it could also be configured to do crew rotation for the ISS (eight crew plus 2 mT of supplies/equipment in one flight), which is actually plausible if they get it operational before 2020 as planned, even more so if the ISS is extended to 2028...

Heh...  the video also suggests using Skylon to fly servicing missions to help extend the station's lifespan...  they claim it replaces the Shuttle's capabilities, which it kind of does, but it can't do crew and heavy payloads at the same time, and it appears the C2 config can only launch about 11.5 mT to the ISS (high orbital inclination really hurts an SSTO)...  Still not bad; 11.5 mT is enough for most contingencies, and later iterations of the design (D1 etc.) might improve on it...

[kkattula]

I'll play, using existing engines and flown tank mass ratios (the Lego method):

SSTO, VTVL, truncated cone.
4 x Merlin 1c
4 x RL-10-A-2

Mass budget in metric tons:

GLOW:  185
IMLEO:  14.7

Propellant: 171
  LOX:  125
  RP-1:  40
  LH2:     6

Engines (inc plumbing and thrust structures)
4 x Merlin 1c:    4.5
4 x RL-10-A-2:  1.5

Tankage:  2.5
  LOX:   1.3
  RP-1:  0.5
  LH2:   0.7

TPS: 0.5
(Bolt on PICA replaced after each flight)

Cabin: 1
Other: 1  (avionics, ECLS, batteries, RCS, etc)

Leaves 500 kg for crew/passengers.

The only armwavium is an assumption of double bell nozzles on the RL-10s so they can be used at sea level for landing. Propellant includes 1 t of LOX/LH2 for landing. Boil-off GOX/GH2 used for RCS.

Launches using the Merlins, which provide 3600 m/s dv, then switches to the RL-10s which provide another 5840 m/s.

Further details left as an exercise to the reader...

[kkattula]

Skylon?

Seconded.

I know it's bad for an engineer to get on a bandwagon and stop thinking, but sometimes I'm amazed at how much effort it takes to get people to even acknowledge the Skylon concept's existence in an SSTO thread...

I guess we'd like to see a SABRE engine actually fly.  Until then, it's just an interesting concept.

As with all SSTO concepts, a relatively small mass budget overrun or engine under-performance would quickly eat up the payload. Using existing rocket engines, the latter is not as likely.

[93143]

As with all SSTO concepts, a relatively small mass budget overrun or engine under-performance would quickly eat up the payload. Using existing rocket engines, the latter is not as likely.

Actually, the engines have to underperform quite severely to eliminate the payload.  The airbreathing portion of the launch takes care of a lot of delta-V and desensitizes the design to small changes in performance.  I did a BOTE calculation here that indicates that you'd have to take the rocket-mode Isp down from 459 s to about 406 s to eliminate the payload, all else being equal.

Structurally, the design seems reasonably well quantified to me - they've got a detailed structural concept, they've selected materials, and they've even designed a water-cooled braking system (that dumps the water after a successful takeoff) to save a few tons of solid heat sink.  IMO they'd have to have screwed up pretty royally to lose a 15 mT payload in a 53 mT dry mass, though admittedly if it did get reduced to 5 mT or something, the initial launch price would be a lot less attractive...

I guess we'll see how the engine development goes...

[mlorrey]

Some VERY rough numbers to guess-timate a demand curve:
At $20-30 million per flight, Russia has sold an average of 1 seat per year.
At $200,000 per sub-orbital flight, Virgin Galactic has 300 pre-orders.
At $1-3 million per flight, I would guess a demand closer to 10 passengers per year or about 1 flight per month at 1 pilot and 1 passenger per flight. I think that you may have trouble making ends meet on a SSTO RLV.

Russia has only OFFERED one seat per year for sale.

At 1-3 million per flight to orbit, the sales would be through the roof. Anybody with the spare change to spend 200k for 5 minutes in suborbital free fall certainly has 1-3 million to spend a week in orbit.