“2) Reentry — Armadillo/Masten are currently testing shrouds for suborbital flight, but the thermal environment involved in orbital reentry is much more challenging.”

I do not know what suborbital velocities they are looking at but it is indeed a lot more challenging. For LEO return you only have to account for convective heat rates. These heat rates go like velocity cube. So if we assume a similar profile and we take VG suborbital velocity at about Mach 3 and we compare that to a LEO reentry of about Mach 25 that gives you, everything else being equal a heat rate about 600 times higher. And the heat rates goes like temperature to the fourth. Of course you have to account for the heat shield radius – below – and materials.

“Per DC-X, there are basic questions about whether a base-first or nose-first reentry are best, on top of designing the specific EDL profile and reentry surface. But hopefully the TPS materials are already in hand.”

This question is related to that above. The heat rates go like 1 over sqrt(radius of heat shield), convective that is. So the larger the heat shield radius the better. Unfortunately for say lunar return velocity the heat rates are augmented with radiative heat rates that go like the radius of the heat shield. During initial reentry at these velocities the radiative heat rates are very large. In summary for convective heating a large radius heat shield is better but for radiative heating a small radius is better. So in the end it all hangs into the material. This is one major reason why you use ablative materials for lunar return, trying to get best of both worlds. The ablative process somehow keep the temperature on the heat shield to go beyond the temperature at which it ablates. For a capsule it is manageable, for a vehicle with say wings it becomes more of a pain since the controllability becomes affected by the surface recession of the heat shield.

Anyway. Reentry is a very complex and painful process. I should note that the shape of your heat shield will make your vehicle more or less controllable and with more or less down/cross-range.

Difficult to give all the issues associated with reentry in a blog entry but you get the picture.

[1] http://en.wikipedia.org/wiki/Reentry

[2] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.75.1042&rep=rep1&type=pdf

[3] http://books.google.com/books?hl=en&lr=&id=NKOIAY_Cj2kC&oi=fnd&pg=PA1&dq=radiative+heat+rates+bertin&ots=s1ms_d_QHT&sig=BdkBFZM8JBqOUyzzXtfssUXKrOE#v=onepage&q=radiative&f=false

Absolutely. Something like Aquarius would certainly be enough for cost-effective government funded exploration, even without cryogenic depots or RLVs. Maybe even for limited private exploration, say by something like the Discovery Channel or the National Geographic Society. And that by itself would likely be a disruptive change.

As my goal I was thinking of something that would enable purely commercial manned spaceflight, with private organisations or wealthy individuals as clients and without the need for cross-subsidies from government funded exploration. Space tourism seems like the most likely initial goal, but it could be something else too. I don’t think space farmaceuticals would be helped all that much by dramatically lower launch costs for bulk materials. I suspect that depends more on cheap EELV-sized launches. Space tourism could work with something in the 5-10mT range and dramatically cheaper than what we have today.

Specifically, RLVs have historically needed high flight rates to amortize their high development costs.

And high recurring fixed costs too. You may need a broader set of skills to operate an RLV, which translates to a larger staff and higher fixed costs. That would still apply to newly developed RLV.

To evolve from today’s Armadillo/Blue Origin/Masten vehicles (which have yet to go suborbital) to an orbital TSTO VTVL RLV, I think three things need to happen, in order of importance/difficulty/cost:

I agree with most of these, but they are not really new technologies. They are existing technologies that these companies would still have to master. I don’t necessarily see these companies as the most promising road to cheap lift, at least not in theory, if NASA were to establish a propellant market, which seems very unlikely, unfortunately. And that’s what I’m really trying to find out. Do you really think there are new technologies that companies like ATK, Aerojet, PWR, LM, Boeing and ULA would have to develop before they could build a minimal RLV of the type I described above? I agree in principle that some degree of technology push might be needed (or merely useful), but I see no hard evidence that it actually is necessary. I’m curious about your thoughts, because depending on whether there are such technologies I might support a different set of policies. Not that the world cares about my opinions, but at least I do.

The LOX/alcohol and peroxide/kerosene engines currently used by Amadillo/Blue Origin/Masten likely lack the Isp necessary to support orbital flight without massive staging (much more than TSTO).

I’m not so sure about the need for different propellants, although pump-fed engines are nearly certainly necessary. Kerolox and kerosene/peroxide are both excellent first stage propellants. Peroxide makes up for its lower Isp by its very high density and very high O/F ratio. I think it is doubtful a first stage of a TSTO RLV would benefit from LOX/LH2.

It depends on what your goal is.

If you’re trying to enable some Bell Labs, Hilton Hotels, and Pan Ams in Earth orbit, then transporting scores or hundreds of people to and from orbit each year as cost-effectively as possible is the driver, and some flavor of passenger-carrying RLV is probably key.

If you’re trying to open up BEO to sustained human space exploration, then cost-effectively staging massive amounts of propellant in orbit or at Lagrange points to fuel departure stages is the cost driver, and something like Aquarius or Quicklaunch is probably key. The crews will be small and bringing them up on an existing asset, like a few Dragon capsule flights, will be more cost-effective than building an RLV for that purpose.

If you’re trying to settle some BEO location — requiring the transport of enormous amounts of propellants and scores to hundreds of passengers — then both are probably key.

“Aquarius could well be wrongly sized for use as an upper stage on a suborbital RLV, but even so cheap mass production technologies could still apply to a more appropriately sized stage.”

Something like Aquarius, where you’re mass-producing launch vehicles, could have some very interesting economic implications for the launch market in general. Because they’re so low-cost, components from a launcher like Aquarius might rapidly find their way into other launchers, supplanting existing suppliers and/or enabling new, more competitive launchers in other segments of the market.

“I see the high flight rates needed for tiny RLVs as a plus: RLVs need high flight rates to be economical.”

Specifically, RLVs have historically needed high flight rates to amortize their high development costs. That’s part of why NASP, X-33/VentureStar, etc. didn’t go anywhere. Even if they had worked technically, to amortize their multi-billion dollar development costs, they had to assume ridiculous launch market capture and launch market growth.

But develop an RLV at a lower cost, and the flight rate can be lower because there’s less to amortize. The low-cost approach to suborbital RLVs that has been demonstrated by the likes of Armadillo, SpaceShipOne, etc. — if it can be successfully transferred to orbital RLVs — may change that equation.

“It’s hard to see how you could make a profit on development of an EELV-sized RLV in the foreseeable future, and I think that is precisely the reason why we don’t have one.”

If the development cost is low enough — less than what was spent on one of the EELVs so the new RLV can amortize and compete effectively — it would make sense but that’s a hypothetical. Falcon 9 may pull it off if its stages can ever be recovered. K-1 also falls into that category assuming it had been able to carry through.

The alternatives are to accept a cost per flight higher than what existing ELVs charge (but it’s unclear why anyone would pay such a premium) or to assume government cost-sharing and/or funded development. Although it’s in a very early stage of design/development, the latter is what the USAF/AFRL are doing through their rocket-back reusable booster system (RBS), which could evolve into a bimese HTHL TSTO similar to Rockwell’s X-33 proposal:

http://www.aviationweek.com/aw/generic/story.jsp?id=news/awst/2010/04/19/AW_04_19_2010_p30-219818.xml&headline=USAF%20Plans%20For%20Reusable%20Booster%20Development&channel=defense

“Do you think any new technology is needed for a minimal, fully reusable TSTO VTVL RLV, capable of reliably carrying at least 0.5mT payloads, capable of 50-100 flights a year”

To evolve from today’s Armadillo/Blue Origin/Masten vehicles (which have yet to go suborbital) to an orbital TSTO VTVL RLV, I think three things need to happen, in order of importance/difficulty/cost:

1) Higher Engine/Fuel Efficiency — The LOX/alcohol and peroxide/kerosene engines currently used by Amadillo/Blue Origin/Masten likely lack the Isp necessary to support orbital flight without massive staging (much more than TSTO). Armadillo has talked about an Otrag-type concept that might get around this, but if you’re limited to TSTO, then different fuels and more efficient (and obviously bigger) engines will be needed. It’s possible some existing engine design might fit the bill with some inexpensive adjustments to enable the necessary throttling (like the RL-10s used on DC-X). But achieving the necessary reusability in a sizeable engine may require a clean-sheet design since all existing engines are designed for ELVs or only a few upper-stage firings.

2) Reentry — Armadillo/Masten are currently testing shrouds for suborbital flight, but the thermal environment involved in orbital reentry is much more challenging. Per DC-X, there are basic questions about whether a base-first or nose-first reentry are best, on top of designing the specific EDL profile and reentry surface. But hopefully the TPS materials are already in hand.

3) Lightweight Structure/Tanks — The everyday steel and aluminum structure and tanks used on the current Armadillo/Masten vehicles are probably too heavy to support orbital flight, even with TSTO. Depending on how efficient the engines are, a move to higher-grade aluminum and maybe some composite structures/tanks may be necessary. Blue Origin is building a composite crew cabin under their CCDev contract so this hurdle may be in hand sooner than the other two challenges.

“and able to match EELV/Falcon launch prices?”

With only a 0.5 ton of payload, it would be easy to match EELV/Falcon price per launch. I assume you mean price per pound or kilogram.

FWIW…

“I am curious as to how he came to the conclusion that 70 to 80 tones is a “sweet spot”. This implies there was some kind of trade study. I would very much like to see the results of such a study. For example, just how much of a penalty would the be for a 50 ton HLV or a 35 ton HLV? Why is the marginal cost of a larger vehicle worthwhile?”

and also said,

“There may well be a knee in the HLV launch vehicle cost curve – a point after which launch vehicle costs rise steeply – but it does not necessarily follow that the overal system (launch vehicle plus payload) optimizes at this size.”

80,000 kg payload to LEO does divide up nicely for some Mars mission architectures, such as the Design Reference Mission 3.0

http://www.astronautix.com/craft/dession3.htm

“He specifically said if a business wants to lease a section of station and turn it into a space hotel for space tourism he would lease them the space.”

This approach is similar to affiliate marketing, which Bigelow would be used to from his hotel days. Essentially Bigelow will leverage off the marketing skills of many companies in order to fill his station(s) – It cuts down on his marketing costs too.

” think Bigelow has correctly judged that LEO tourism on a significantly bigger scale than what we’ve seen to date is not feasible at current launch prices. “

Bigelow has addressed tourism several times in interviews I have watched. He doesn’t want to be in the hotel business but rather a wholesale provider. He specifically said if a business wants to lease a section of station and turn it into a space hotel for space tourism he would lease them the space. He doesnt want to be involved in creating individual space businesses rather just wants to be the wholesaler of space so all the other businesses can do the specialty types of businesses.

Do you think any new technology is needed for a minimal, fully reusable TSTO VTVL RLV, capable of reliably carrying at least 0.5mT payloads, capable of 50-100 flights a year and able to match EELV/Falcon launch prices?

Thanks for the detailed replies. This is the kind of discussion I wish we had more often on forums like this.

I agree Aquarius isn’t suitable for humans, which is why I’m somewhat wary of it: it could end up outcompeting RLVs for propellant, which would still leave us without a cheap way to launch humans to orbit even if NASA did establish a propellant market. Aquarius could well be wrongly sized for use as an upper stage on a suborbital RLV, but even so cheap mass production technologies could still apply to a more appropriately sized stage. Given the lower delta-v you could buy back margin and reliability if you wanted to, or not if all you wanted to do was to launch propellant.

I see the high flight rates needed for tiny RLVs as a plus: RLVs need high flight rates to be economical. It’s hard to see how you could make a profit on development of an EELV-sized RLV in the foreseeable future, and I think that is precisely the reason why we don’t have one.

I don’t disagree with your logic in general, but I would point out that Aquarius is a SSTO expendable. So the Aquarius system specifically might not have much synergy as the expendable upper-stage for an RLV booster.

“LEO space tourism seems like the most probable commercial market for manned spaceflight to me. But who knows, maybe orbital manufacturing is possible too. Do you think it is likely that will turn out to be profitable?”

Depends on the timeframe — anything is possible if the calendar runs long enough.

And it also depends on what you mean by “manufacturing”. There are very different infrastructures and workforces involved in, say, identifying drug targets using suitcase-sized biochemical arrays in microgravity versus, say, making tons and tons of some useful nano-material in microgravity.

The former kinds of applications — small/low-power/limited Earth-return — will probably emerge as the first commercially successful space-manufactured products than the latter kinds of applications, which have large/high-power/big Earth-return requirements. This is simply because the kind of transportation and in-space infrastructure needed for the former is much easier and less expensive to achieve than the latter. We’ll probably see nanosatellites with very small automated reentry vehicles running drug target arrays for Amgen or Pfizer, for example, before we’ll see tons of super-material manufactured at a large space station and brought back down by RLVs for 3M or Dupont.

I’m similarly skeptical of most ISRU in the near-term for the same reasons. Achieving the scale of product necessary to have an impact using the scarce and apparently widely scattered resources we see at the Moon (and probably NEOs) will require the expensive development, erection, and operation of a large and unique infrastructure, on top of the cost of transporting that infrastrcture from Earth to the destination. It’s hard to see that competing eocnomically with just buying and launching existing terrestrial sources/products from Earth, even with the Earth’s inferior gravity well, for a long time to come. Even really efficient ISRU thinkers like Zubrin or the old t/Space team require things that are currently prohibitively expensive, like nuclear power sources on the surface of the Mars or Moon, to gather and process enough of the relevant resource. Doesn’t mean that we shouldn’t continue (or even step up) prospecting robotically. But we havn’t identified the resources or technologies for the U in ISRU to make economic sense (or, at least, I havn’t seen such).

Of course, I’m trying to play realist/skeptic/devil’s advocate on all the above. I personally like to see it all happen sooner than later.

My 2 cents… FWIW.