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A number of companies are working on suborbital flight with Blue Origin, Virgin Galactic and XCOR being among the most recognized today. I don't ask here about what actual plans different companies have, but at first look a plausible strategy could be to start out with a suborbital launch system with the aim of developing an orbital launch system out of it.

Is suborbital flights a natural stepping stone to orbit? (In our time, the early space race is a bit OT). Can the same engines, whole stages, crew capsules be used both in and sub orbit? Or are there difficult compromises which risk leading to both the suborbital and the orbital systems becoming suboptimal? For Virgin Galactic and Virgin Airline (suborbital and airlines) the synergies are not obvious to my mind, maybe the step to orbit is as big.

Sub-orbital systems which are up and coming, if they become successful, are mostly crew oriented (while sounding rockets with science payloads and ICBM's are well established and less commercial). So a strategy to begin with sub-orbital flights seems to me to require crewed flights, if the sub-orbital business leg is to generate a profit of its own. If that is correct then I suppose my question is whether it is basically rational to approach crewed orbital launches from crewed sub-orbital launches, and maybe even building on airline experiences. Will sub-orbitals get important advantages over those who go for orbit directly, or are they suboptimizing by trying to do two different things?

Airborne launches (like VG is planning), VTOL and winged spacecrafts and parachutes into the ocean and whatnot are all plausible technologies. I don't want to directly address them per se in this question about the synergies and differences in going from (or via) sub-orbital to orbital. Could for example the same launch pad and ground operations be used?

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  • $\begingroup$ Could you be a bit more precise please? One example of a company with cross-over plans is the Virgin Galactic effort for Space Ship 2 and Launcher One. This really needs a clarification from you as to what you want as you have not limited your question explicitly to crew carrying ventures but have not mentioned any unmanned systems either. $\endgroup$ – Puffin Jan 30 '16 at 12:11
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    $\begingroup$ I guess you are already aware that the energy involved in both launch and re-entry/landing are an order of magnitude different and the safety case similarly so as you have to assure the regulator that you won't land outside the range vs anywhere on the planet. My personal tuppence: I suspect the area of greatest similarity is in private funding streams where institutional investors neither understand nor care about the design solution, trade-offs, safety etc. $\endgroup$ – Puffin Jan 30 '16 at 12:16
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    $\begingroup$ @Puffin I added a paragraph where I suggest that (commercial) sub-orbital launches require human spaceflight in order to have a market. Concerning the order of magnitude difference, maybe a sub-orbital launcher could use an order of magnitude more of the same engines. Like SPX went from 1 to 9 Merlin engines, and will attempt 27 (although orbital to begin with). $\endgroup$ – LocalFluff Jan 30 '16 at 12:37
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    $\begingroup$ @Puffin Oops! It didn't turn up on my brief search. And my memory is short. Especially since I don't have seen any really good explanations of the trade offs involved. The great variety in approaches indicate that it is a topic of ongoing entrepreneurial discovery. But I thought that something fundamental could be said about it. $\endgroup$ – LocalFluff Jan 30 '16 at 13:10
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    $\begingroup$ This isn't my territory, hence my lurking in the comments rather than trying to put a full answer together though I have noticed this, space.stackexchange.com/questions/8026/…, which might provide some inspiration for someone better qualified to elaborate on the question of "sub-orbital => is heat-shield needed?" $\endgroup$ – Puffin Jan 30 '16 at 13:16
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Sub-orbital space flight as a step on the road makes sense, at least for a commercial space program. You can then scale up your business along with your development process. The most notable disadvantage is that you will not be able to launch satellites, forcing the company to focus more on manned space flight.

In contrast, the main focus of the early space-programs was to develop an ICBM as soon as possible (In the business world, nuking competing companies are frowned upon). That means that resources are channelled into completing an orbital launcher. When the Soviet union had an orbital launcher, they decided to just skip a manned sub-orbital program. As a consequence, the first human in space, Yuri Gagarin, went on an orbital mission.

But the manned spacecraft developed for sub orbital flights are not necessarily fit for orbital missions. They tend to be more like aircraft and less like minimum mass capsules, and in any case, a lot of new requirements must be met, like heat shields. Winged orbiters are not necessarily a good idea, as they tend to mass more and have a more complicated design. The space shuttle for instance was never capable of providing a reasonable launch cost.

However, a space program is not just the spacecraft on top, almost everything else, like launch pads, rocket engines and mission control can be transferred directly into an orbital space program. Sub orbital flight is definitely not a dead end.

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    $\begingroup$ never forget the $v^2$ in the kinetic energy equation. A suborbital craft of 1km/s lateral velocity has 64 times less energy to dissipate than an orbital one of 8km/s. $\endgroup$ – SF. Jan 30 '16 at 18:30

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