The Road To Suborbit

Henry Spencer is describing the technical issues of the realm between low suborbit and orbit. His bottom line (which which I agree): there’s not a lot of market to justify investment for mid-range performance, including ballistic trajectories, because they need almost as much performance as orbit.

Thinks that there may be a role for suborbitals as a first stage for nanosats, and it may be possible to make some money on it, but they’re not going to be willing to pay a lot for a launch, particularly considering that piggybacking on orbital launches isn’t that expensive. Not a lot of utility to cubesats to date, most of them “solar arrays with radios.”

[Update a while later]

Sorry, there was a whole lot of other discussion, but it wasn’t completely jointed, and I was distracted. I saw Clark Lindsey taking notes, though, so I’ll bet he’ll have something posted later this evening.

Sure enough, here it is. He also has some notes from the later afternoon sessions.

5 thoughts on “The Road To Suborbit”

  1. Except that suborbital passenger flights could potentially be a lot bigger than orbital flights over this century. For example, subsonic flights between Los Angeles and Melbourne, Australia are more than 15 hours long. Cutting that down to say, 2 hours would generate some degree of demand. If suborbital flights could be as cheap and safe as regular passenger flights, they would take the entire demand (unless a hypersonic competitor was even better).

    Even if flight to orbit got as cheap as international fare on an airline, it’ll still be quite some time before there’s anything significant to fly to in orbit.

  2. And, I think probably bigger, is package shipping. Don’t underestimate the value of getting papers to complete a merger to another continent that need first-hand signatures from both parties on each document and wrapping it up before the competition knows it, or shipping small, high-tech, specialty parts to something like a power plant where an hour of outage can be millions of dollars of revenue. It may not be high volume, but the value may be there to justify high operating margins. The person most blown away by these scenarios wasn’t a “space advocate”, but the CEO of an international company who was at the 2007 X Prize Cup with me.

  3. Karl: the problem with ballistic suborbital flights at large distances is the gee loads. On the minimum energy trajectory, the reentry is too steep for passengers to survive. You can get around this by doing a series of skips (in effect, chaining together multiple short suborbital hops), but then your vehicle has to either have good hypersonic L/D or some kind of hypersonic airbreathing propulsion, or both. Or, you could have a depressed trajectory, but that gets close to orbital velocity anyway.

  4. Paul

    The Gee loads for Long Distance P2P is one thing
    that can adjusted by either using Lift (As you point out)
    or by using thrust. You have engines, you can
    use them to cut the G loading down but that does
    push you against the other limit. Mass Fraction.

    Long Range is all a Mass Fraction issue, and,
    when you talk intercontinental you are at 85%
    of orbit. It’s why our ICBM’s all got made into
    Orbital launchers. They were almost there anyways.

    now if we have flying short haul Suborbitals,
    the range will slowly keep extending.
    The natural improvement in Orbital capacity
    dictates a down range run, that will over time
    evolve into Package delivery. As the
    Booster becomes more capable, the
    upper stages will become cheaper.

  5. “On the minimum energy trajectory, the reentry is too steep for passengers to survive.”

    Don’t use a minimum energy trajectory- waste rocket fuel.
    On reentry you could slow your descend using rocket power, so perhaps one has a result of about 1/2 of these high gees.

    Or instead of efficiently using the the atmosphere with exotic scram jets for a series of hops, again waste rocket fuel doing the same thing without involving the higher atmosphere providing additional lift and capturing rocket propellent.

    Suppose your suborbital vehicle had 3/4 of the delta-v of a rocket going to orbit. Instead of traveling at around 6 km/sec, it travels at around 4 km/sec [8900 mph] and uses +2 km/sec of that delta-v to keep it above the atmosphere.
    At 4 km/sec you will travel +2000 miles in 15 minutes [900 seconds]. Assume this rocket thrust for the +2 km/sec is less than one gee for about 10 minutes [600 seconds], so this rocket power would be not enough to to cause the vehicle to hover in 1 earth gravity, perhaps it’s a 1/4 to 1/2 a gee of thrust.

    But as far as traveling somewhere vs joyrides with suborbital, you probably want to start with 500 to 1000 mile distance, and therefore about 1/2 of delta-v as what it takes to get to orbit.

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