Suborbital trajectory as compared to different altitudes.
(Source X PRIZE)

For the article Suborbital spaceflight: a road to orbit or a dead end? - The Space Review - Dec.15.03, I sent the following question via email to several aerospace experts:

Could you list the top 3 or 4 reasons why you think (or don't think) that the development of commercial suborbital RLVs will contribute directly or indirectly to the development of orbital RLVs?

In the article I only gave selected portions of their responses and paraphrases. Below I show the full text of their replies with some minor editing and formatting changes.

• Pat Bahn
• Len Cormier
• Henry Spencer
• Dan DeLong
• Mark Oakley

See also comments on suborbital spaceflight in my interviews with Elon Musk and Gary Hudson and
Reader's Comments on the article.

Pat Bahn: Founder and chief of TGV Rockets and long time champion of suborbital RLV development.

My basic feeling is that Suborbital has implications for Orbital development in the same way that the 8 Bit Micro-computer from Altair had implications to the mainframe computing industry.

Micro-computers served to train whole legions of students on binary aritmetic, boolean algebra, logic, programming, hardware design, board design, product maintenance, meanwhile creating an entire industry that with internally generated R&D developed billions of dollars of new technology
ultimately surpassing the mainframes.

Consider the computer from IBM in 1970. $10M each, Giant room, Huge enviropnmental process control, 3 phase 207 V, 400 Hz input ,dozens of people feeding disk farms, tape libraries, printer rooms and Input devices. Consider the Imsai 8080 of that time. $2,000 Machine, 110V input, Dot matrix printer, Nerdy white high school kid driving it forwards.

How did it change the game for mainframes? Never. Ultimately the mainframes went away almost entirely, to be replaced by server farms of Commodity boxes, and small data warehouses, with a little climate control and surveillance cameras.

Suborbitals will never affect the technical base of the Orbital ELV, but it will become better in whole new ways and change the rules of the game.

How will this game change?

1. Suborbital RLV's will alter insurance regimes.
2. Suborbtial RLV's will eliminate billions of infrastructure as seen at KSC, VAFB and Kourou and Baikonour.
3. Suborbital RLV's will train legions of new entrants.
4. Suborbital RLV's will create new suppliers.
5. Suborbital RLV's will allow new ideas such as Orbital Skyhooks to allow orbital transfer.

It's about allowing increased revenue, R&D and new entrants.

[Update Dec.15.03: Pat writes "A little thought on the subject indicates skyhooks aren't a very good idea, however, once working suborbitals get going, smart people will figure out ways to use them in such new and exciting ways that it won't really matter how they are used."]

Len Cormier: Head of Tour2Space and the Panero X PRIZE team, Len has been in the rocket design business since the 1950s. (He also consults with TGV and helped to design their vehicle.)

I am not a strong fan of suborbital, since 100 km at relatively low speed is a place to avoid when trying to get to orbit. Suborbital--low-delta-vee suborbital-- is not likely to contribute much technically to an orbital space transport. However, I go along with the suborbital game for the following reasons.

1). It is easier to do, and there are some potential applications. I do think that the ratio of usefulness to difficulty is higher with orbital systems than suborbital systems; however, the investment barrier is much higher. Moreover, trying to raise money for any commercial endeavor is probably the biggest barrier for would-be space entrepreneurs.

2). The X PRIZE presents a different type of opportunity for obtaining investors and/or sponsors. I would have preferred a prize for an orbital system; however, the X PRIZE founders--probably rightfully so --felt that this would require too great a leap.

I would be hard pressed to come up with more reasons, since I am much more oriented toward the orbital camp.

Follow up questions: Would frequent (weekly and eventually daily) suborbital flights help to develop operational techniques and technologies that would later apply to orbital systems, i.e. make them more robust and lower cost? Especially with regards to reusable propulsion systems?

Similarly, could the technology of a suborbital vehicle apply directly to the first stage of a two stage orbital system? (I'm thinking more about manned orbital than just shooting smallsats into orbit like RASCAL.) For example, might a Michelle-C, derived directly from Michelle-B, become the first stage for a small two stage manned (say 2 passenger) orbital system?

With respect to applicability of suborbital developments to orbital systems, some items such as robust, highly reusable rocket engines and some turnaround operations could obviously benefit orbital systems. But otherwise, I think the benefits are limited. I personally would rather attack the orbital systems directly--if the funding is available--a big if, I admit.

As for Michelle-Charlie, yes, I think this version has potential for higher delta-vee missions. However, that is Pat Bahn's department: marketing of other potential applications for Michelle. As you might guess, Pat and I have a certain amount of friendly disagreement with respect to suborbital versus orbital systems. I obviously don't discount the potential of suborbital systems. Otherwise, I would not work closely with Pat and support his effort.

Henry Spencer: Henry, who gives an overview of rocketry at the beginning of every Space Access Society conference, is renowned for his encyclopedic knowledge of rockets and spacecraft.

My take on this is "no, well maybe, well actually yes".

No:
It's certainly true that getting into orbit is a much harder problem. In early-aviation terms, it's the difference between barnstorming and flying the Atlantic. Many of the same technologies are applicable, but the numerical requirements are much more demanding. Even a company which has built and is operating a suborbital RLV will have to design a completely new vehicle for orbital operations, and the orbital vehicle will probably share only incidental bits of hardware with the suborbital one.

Maybe:

Bear in mind that a 100km apogee is not a fundamental limit on suborbital flight. When you start pushing for higher altitudes, and possibly also longer ground distances covered, the problems get harder and the disparity between suborbital and orbital shrinks. For example, you start needing real TPS; the TPS systems used for the first orbital vehicles (capsules) were simple derivatives of those used on suborbital vehicles (ICBM warheads). The question about this approach is whether the greater performance enlarges the suborbital market enough to pay the development
costs of the hotter vehicles.

Yes:

1. Company credibility. This business has always had a problem with convincing potential investors that you can actually deliver on something innovative, especially given the tendency of certain large companies and government agencies to exaggerate the difficulties. Delivering and operating a suborbital vehicle as promised will go a long way toward establishing technical credibility for later promises.

2. Development and operations experience. Granted that a suborbital vehicle is different from -- and easier than -- an orbital one, a team which has done the former will have a much better idea of how to do the latter *right*. Studies and viewgraphs are no substitute for experience.

3. Flight-test options. Being able to test orbital-vehicle systems in space on a suborbital vehicle will be a significant advantage. Some will be upgrades to the suborbital systems, while others will have to fly as payloads, but being able to try things out in their real operating environment -- even briefly -- will help a lot.

4. Regulatory experience. A company which has established to the FAA's satisfaction that it can build and operate suborbital vehicles safely is going to have a rather easier time convincing the FAA that it can do orbital vehicles safely. Issues like reliability cannot be settled by reasonable numbers of flight tests; they are fundamentally a question of
confidence in the company and its engineering process. Doing it once will make it much easier to do again, and will also greatly simplify convincing investors that you'll be *able* to do it again.

> I've seen statements from Alan Bond, John Pike, and others that are scathing towards suborbitals.
> They primarily focus on the factor of 25 or so greater energy needed to reach orbit and the far tougher TPS
> requirements.

I think these folks are making a fundamental mistake. They're assuming the traditional model of rocket development, where huge amounts of money are poured into building a system with absolute maximum performance, and into making "certain" that it will operate perfectly the first time. While this approach *has* been standard in the past, it is horribly expensive... and worse yet, it doesn't actually work very well.

Notice that their objections are essentially on technical grounds, where none of the four points I make above is really technical. In the old model -- government-funded development of artillery rockets -- technical problems dominate. In the harsh, cold real world that commercial rocket projects face today, *the technical problems are not the hard ones*.

Dan DeLong: Dan is Chief Engineer of XCOR Aerospace and one of the founders of the company. It was Dan's EZ-Long that became the EZ-Rocket. (See this article from Sport Aviation for more about Dan and the EZ-Rocket)

There are several reasons why reusable, operable, low cost suborbital vehicles will evolve into orbital systems. Suborbital RLVs are easy to test frequently. A typical new airplane design is taxi tested, then makes runway flights before expanding the envelope. The flight test program typically does only one new thing per flight, and the vehicle and crew are usually recovered if the test goes awry. Taking this philosophy to an orbital system requires early suborbital flight testing. Just as each vehicle is tested in increasingly difficult environments, so can the evolution of vehicle designs grow until orbit is reached.

The organization doing suborbital space flight gets the benefit of developing a team that will go on to do more difficult missions later. (This is an example of reducing management risk as opposed to technical risk.) The teams that can show low cost and reliable suborbital operations have the best chance to evolve higher performance vehicles. Reusable vehicle developers get practice designing materials and systems for the space environment.

An operational suborbital RLV will make a good reusable first stage for an ELV upper stage. This "flyback booster" will cut the cost of getting near-term satellites into orbit. One might argue that this IS an orbital vehicle, performing an orbital mission.

Incremental performance extension is the only way that major transportation services have EVER developed. Early automobiles were expensive, unreliable toys for the rich, and for army scouts. They've been developing for over 100 years and they're still getting better. Early trains had horribly inefficient, low power locomotives, manual brakes set on each car, and per-ton-mile real costs many times higher than today. Steady improvements over the past 170 years were done by the profit-making owners, not government agencies. The first airplanes were barely able to carry the pilot at speeds slower than other contemporary forms of transportation, but nobody thought design should stop until transatlantic flight was viable.

Why should space flight be different? Just as Mercury Redstone sent Alan Shepard and Gus Grissom on suborbital flights before Mercury Atlas orbital flights, so will low cost, robust commercial suborbital flight operations lead to low cost commercial orbital flights. The oft-quoted 25X energy requirement for orbital flight is a misleading number. Attaining high vehicle energy is largely a function of mass ratio and specific impulse. If the energy requirements can't be met, adding stages has been the traditional way to get the job done. Similarly, many aspects of an orbital reentry thermal protection system (TPS) can be tested on a suborbital vehicle. Real-world operations in rain, repeated heat/cool cycles, and maintainability aspects of TPS can be tested suborbitally. Certainly, the peak temperature profile will not be modeled, but this is not the only requirement for robust TPS.

In addition to the engineering reasons, there are financial and marketing development issues as well. XCOR developed the EZ-Rocket as a cost and operations demonstrator. Its marginal flight costs are under $1,000. This allows us to predict Xerus costs with some confidence that we can make money at the market price for a vehicle of its capability. As a small company, we do not have the ability to develop a manned orbital system. But after Xerus is making money, we will.

Mark Oakley: Mark is a Senior Engineer at Lockheed Martin's Engineering Propulsion Laboratory and has worked on many rocket projects including the Atlas V. Mark is also known as for his Rocket Man Blog website.

1: To answer your question, yes I do believe that private commercial suborbital RLV development can contribute to the development of orbital vehicles and here's why. Large companies are not very good at creating new markets. What they are good at is exploiting existing markets. As long as the launch vehicle market remains exclusively the province of large companies and governments, the
existing uses for launch vehicles as satellite launchers and space station taxis will not be added to anytime soon.

Private commercial suborbital RLV's on the other hand are being developed to create new markets or exploit existing markets that the large companies are not servicing very well. Space tourism and sub orbital missions are just two of these markets, but vehicles that can fly anywhere in the world in around two hours would open up new opportunities like fast passenger/package delivery or military bombers that could be based in the United States and quickly reach anywhere in the world.

The routine commercial use of sub orbital vehicles would in turn contribute to the development of orbital vehicles by maturing the technologies needed for such vehicles and by creating the infrastructure needed to build and support them.

I hope this helps. If you have any questions, please respond to my home email address (rocketmanblog@earthlink.net) and not this one (it's my work address, and I can't access it from home).

2:
To answer your question, yes I do believe that private commercial suborbital RLV development can contribute to the development of orbital vehicles and here's why. Large companies are not very good at creating new markets. What they are good at is exploiting existing markets. As long as the launch vehicle market remains exclusively the province of large companies and governments, the existing uses for launch vehicles as satellite launchers and space station taxis will not be added to anytime soon.

Private commercial suborbital RLV's on the other hand are being developed to create new markets or exploit existing markets that the large companies are not servicing very well. Space tourism and sub orbital missions are just two of these markets, but vehicles that can fly anywhere in the world in around two hours would open up new opportunities like fast passenger/package delivery or military bombers that could be based in the United States and quickly reach anywhere in the world.

The routine commercial use of sub orbital vehicles would in turn contribute to the development of orbital vehicles by maturing the technologies needed for such vehicles and by creating the infrastructure needed to build and support them.


I followed up with a second question:

With regard to "maturing the technologies", would you agree or disagree [with the] following:

If a company develops, say, a 30k lb thrust engine design that flies
several hundred times safely in suborbital mode, it is bound to be in much
better position to develop a robust, reliable 300k lb reusable engine for
an orbital booster than if it had gone straight for the high power engine.

I have given some thought to your question and I have to say at first I thought yes, definitely. But after contemplating it for a while, I have to say I'm not sure. I think any experience with making a reusable engine would help in making another reusable engine, but I don't think size necessarily matters. Large engines scale pretty well and the cost of designing/testing/building a 30k engine would not be orders of magnitude different from making a larger engine, although the smaller engine would definitely be cheaper. This smaller cost would allow you to spend more time (assuming the same budget) developing the smaller engine than the larger engine, but I don't think developing a smaller engine is necessarily a prerequisite before you develop a larger engine. The main argument for developing the smaller engine first is that it can be done cheaper than starting with the larger engine and thus has a higher probability of actually being built.

Readers Feedback

Hi Clark, That is a great article you just published for SpaceReview

[article description & link].

May I quickly offer these two articles for you to consider as supplements or follow-ons? These deal with the question of orbital launch costs. (Apologies for the title of the second article).

Fred [Becker]

1. Why Are LAUNCH COSTS So High?
Peter A. Taylor
murmur@ghg.net
March 2000

"Why do space launches cost so much? Specifically, why are the costs so far out of line with the cost of seemingly comparable airplane operations? Fuel is about 15% of the operations and maintenance (O&M) cost of a typical military airplane, and 38% for commercial aircraft, according to Aircraft Design: A Conceptual Approach, 1992, by Daniel P. Raymer. Space launches should be more energy intensive than airplane flights, so one would expect that propellants would be a larger fraction of the total operations cost for a launch industry that was as mature as the airline industry. Why are the non-fuel costs orders of magnitude higher for rockets? "

http://www.ghg.net/redflame/launch.htm

2. We Don't Need No Stinkin' Technology
By Rand Simberg
simberg@interglobal.org
Thursday, August 08, 2002

"It turned out that, for a given set of mission requirements, there were minor differences in cost from one vehicle design to another, or from one technology choice to another. But there were huge differences in cost when you went from a small market size to a large one...."

http://www.foxnews.com/story/0,2933,59889,00.html