FLEX – Flexible Exploration Architecture

I wrote this architecture proposal, FLEX, a few years ago. It analyzes NASA’s approach that the ESAS study picked and notices how most of the mass in a lunar exploration stack in LEO is actually liquid oxygen. By using a propellant depot, the LOX can be lifted with tankers and any launchers imaginable (I wouldn’t use a Pegasus though). The rest of the stack is also naturally divided into about 20 ton chunks: EDS with its hydrogen, the CEV crew vehicle (Orion) and the LSAM lander (Altair).

No new heavy lifters need to be developed, there is enough US, nevermind world launch capability to support a moon exploration program. Launchers can also be improved on the run, because they are not tied to the single use, nor is the use dependant on the single launcher, and because they can fly often, hence improvements are worth the investment. This all could be achieved much sooner and cheaper than the current approach, and is much more robust for the future.

Go read it if you haven’t.

There are some comments at an old Nasaspaceflight.com thread that deal with a lot of the common questions about it.

I really don’t have the faintest idea of the background knowledge level of the readership here so I don’t know how much basics I should give, so feel free to ask in the comments if anything is unclear.

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17 Responses to FLEX – Flexible Exploration Architecture

  1. .

    the orbital-refuel supporters are completely blind about this technology!

    infact, they (often) are the same guys that support crazy things like SSTO, Air Launc, Space Solar Power, etc.

    the basic principle of orbital refuel is not bad at all, since, refuel and reuse the very expensive space-hardware, always IS a very good thing

    but the MAIN problem of the orbital refuel is today’s (very high) PRICE of LEO launches!

    I try to explain my point

    we know that, all best and reliable rockets (like Atlas, Delta and Ariane) can launch a payload to LEO at prices around $20,000 per kg. …NO MATTER if the payload is a satellite or a tank of propellent…

    SpaceX just “hope” (so far) to reduce this price to $10-15,000 per kg. that, unfortuntely, STILL is too high

    so, if you launch a capsule with a big rocket and its full EDS propellent OR launch the same capsule and EDS empty and refuel it in space from a space-gas-station the TOTAL price always IS the SAME

    that, since, to send in space the gas-station and its refuel-propellents you “PAY” the SAME “price per kg. to LEO” of a big rocket launched with “everything inside it”

    also, you must add the problems, risks, costs, extra hardware, etc. derived from develop, build, launch, assemble and repair the space-gas-station and its propellent

    the orbital refuel adds two further problems/costs to a space mission, since:

    1. great part of the propellents stored in space will boil-off, so, you must send in space MORE propellents for the same mission (the propellent for the EDS + the propellent lost)

    2. all space operations are very risky and complex, so, a mission that needs several launches, several rendez-vous, several docking, several assembly, several refuel, several undocking, etc. has (also) SEVERAL TIMES the risks to FAIL than a (simpler) one-launch mission

    you may say that everything may change if the refuel propellents will be launched in space at cheaper price with REUSABLE rockets… but its NOT TRUE, since, you can use the SAME reusable rocket to launch a fueled vehicle at the SAME price and with less risks and problems than a refueled-in-space mission!

    the space-refuel will give a BIG advantage ONLY if we use lunar ISRU (or propellents-only-tanks send from Earth) to refuel a REAUSABLE lunar lander (with hardware costs savings in the range of 30 to 70%)

    that’s why, the orbital refuel is just a CRAZY and USELESS idea TODAY

    however, a small-scale orbital refuel may solve some of the Ares-1 problems as explained in this article:

    http://www.ghostnasa.com/posts/011orbitalrefuel.html

    .

  2. gravityloss says:

    Okay, I was assuming this point was clear to everyone and was not worth mentioning. Of course the total mass sent to orbit is the same (minor efficiency differences might be).

    The reusable rocket would have to be huge, maybe 6 times the size of anything flying today (besides STS), to launch everything at once fully fueled, and also would only launch maybe once or twice per year, making the reusability not worth it. It would also be useless for any other uses because it would be too big.

    But if you do many flights with a smaller reusable, or even many different ones, the cost per flight can be small since the rocket is smaller, you need less crew etc…

    The cost of an RLV is the not that different whether it flies once per year or ten times per year. Hence better make an architecture where it flies ten times per year if you save elsewhere. Or actually, a hundred. And this works by making it smaller (maybe 10 t to LEO), which makes it cheaper to develop and usable for other purposes too, like launching satellites.

  3. just to add, that, the (thousands times more expensive than propellent) parts of a lunar mission (Orion, Altair, EDS) are always LOST in (both) fully-fueled OR refueled-in-space missions!

    so, where is the advantage?

  4. gravityloss says:

    Basically, the more times you fly, the lesser the cost per flight becomes.

    RLV:s are not useful unless you fly really a lot. Moon exploration, both depot filling and hardware delivery is an ideal market for RLV:s, since the payload is already divided into nice size chunks.

    I don’t know how to explain this better. Maybe someone else can try. It is honestly a bit surprising to me that this concept is so hard to grasp for many.

    Of course making more launches by just launching empty rockets doesn’t make flying in total cheaper, since you have to pay for the empty launches too.

  5. but the sum or costs of the small rockets launched to refuel the big (but empty) vehicle will be higher than a single rocket and everything will be LESS reliable

    the orbital refuel goal is to have cheaper space missions… but the BEST way to reach the SAME goal is (simply) “build cheaper rockets”

    the very high costs of the space missions come (99%) from the high costs of the space hardware and NOT from the lack of a space-refuel system

  6. gravityloss says:

    The more Altair and Orion fly, the more they are worth making reusable as well. Especially Altair with in space refueling. It could stay in EML2, like outlined as a future possibility in the FLEX proposal. Anywhere anytime capability, both from and to earth and from and to the lunar surface.
    That is not possible with low lunar orbits (which are not stable either).
    Also fuel usage with L2 is very small.

  7. gravityloss says:

    Why would the sum of costs of the small rockets be higher than a single rocket?

    The small rockets already exist.
    A big rocket must be developed, spending billions and billions.

    The small rockets can be improved, since the architecture is not dependant on one small rocket.
    The big rocket is completely mission critical and can not be tampered with.

    The big rocket has a big standing army that needs it salaries paid even if it flies once or twice a year.
    Meanwhile the small rockets’ crews are working all the time since there are launches all the time. There are more launches per lunar mission. When there are no lunar missions, they launch satellites.

    The small rockets are worth making reusable, since they are less costly to make changes with and try reusability approaches because of their smaller size. Also, reusability gives big savings in a smaller (let’s call it medium size, 10 t to LEO) rocket that flies tens of times per year. But it doesn’t give any savings in a rocket that only flies once or twice a year, in fact it will probably cost more than a throwaway rocket.

    An RLV has to be sized to the market. The lunar market doesn’t support a 180 t to LEO RLV.

    If there is a real market with multiple entrants launching propellants, that encourages improvement and competition. There is safety and redundancy too. Not so with a single big government rocket.

    Having multiple approaches is the way of constant improvement of the future. Having a single government expendable megarocket is the way of stagnation and historical emulation.

  8. as already said, I agree about the advantages of a REUSABLE Altair (especially if refueled with lunar ISRU propellents) but not with a refueled EDS and Orion, since, both are LOST in EVERY mission (no matter if fueled on Earth or in space)

  9. “The small rockets already exist.”

    but no one of them under $20,000 per kg. to LEO
    that sounds VERY expensive to carry propellents

  10. Gabriel says:

    You are wrong Gaetano… Small rockets under the 20000$ /kg to LEO already exist. Search on the Space X site for the Falcon 1e… 1010 kg to LEO for 9,1 M$ (9009 $/kg). And when the Falcon9 will be available it’s 12500 kg to LEO for 36,75 M$. And you completely missed the principal interest of the fuel depot.

    With it, you can launch much bigger ships with already existing commercial rockets, launching them empty. Say you launch an empty 20T vessel to LEO with a classic existing rocket, this 20 T empty ship could include tank capacity for 100T (or more) propellant if you like. You would have a 120T ship when refuelled. If you had to lift it fuelled, even the Ares V or Saturn V wouldn’t cope. Think of it, the ratio tank capacity/tank weight is big (shuttle ET weights 58,500 pounds empty and carries 535000 gallons LOX LH).

  11. @Gabriel

    “already exist” means they EXIST NOW that’s NOT TRUE

    the Falcon-1 has just accomplished its first successful flight and its (expected) price per kg. to LEO is between $11,754 and $15,556

    http://en.wikipedia.org/wiki/SpaceX

    assuming they’ll be able to offer a launch for 9009 $/kg. it will still be HIGHER than russian, indian and chinese prices and always TOO HIGH to carry “cheap propellents” to LEO

    lower prices “should” be achieved ONLY if the SpaceX will succeed in its effort to develop REUSABLE rockets, that’s just an “HOPE” so far

    but, if a reusable rocket will be available (someday) the price to launch a vehicle and its propellents with ONE rocket or SEVERAL rockets (one for the vehicle and many other for the propellents) will be the SAME or higher (and LESS reliable) for the refuelable vehicle option

    the orbital refuel just “SEEMS”, “LOOKS”, “SOUNDS” cheaper, since you (and all other supporters of this concept) ALWAYS use the “trick” to compare the price of a vehicle with its propellents launched with an EXPENDABLE rocket vs. a refuel propellent launched with REUSABLE rockets

    but, if we have a REUSABLE rocket, we can (simply) use it to launch (both) vehicle AND propellents with the SAME rocket at the SAME price (or lower) and the SAME reliability (or much higher) of a multiple launches missions (vehicle + several refuel rockets)

    about your claim that “With it, you can launch much bigger ships with already existing commercial rockets, launching them empty.” that’s true if you refer to the DIMENSIONS but NOT TRUE if we look at its TOTAL PRICE

    in other words, the bigger vehicle refueled in space may carry the SAME payload to the Moon at the SAME price of SEVERAL smaller vehicles launched FUELED form Earth, that, since (today) the “price” to launch “one ton of vehicle” OR “one to of propellent” to LEO is THE SAME

  12. @Gabriel

    “already exist” means they EXIST NOW that’s NOT TRUE

    the Falcon-1 has just accomplished its first successful flight and its (expected) price per kg. to LEO is between $11,754 and $15,556

    en.wikipedia.org/wiki/SpaceX

    assuming they’ll be able to offer a launch for 9009 $/kg. it will still be HIGHER than russian, indian and chinese prices and always TOO HIGH to carry “cheap propellents” to LEO

    lower prices “should” be achieved ONLY if the SpaceX will succeed in its effort to develop REUSABLE rockets, that’s just an “HOPE” so far

    but, if a reusable rocket will be available (someday) the price to launch a vehicle and its propellents with ONE rocket or SEVERAL rockets (one for the vehicle and many other for the propellents) will be the SAME or higher (and LESS reliable) for the refuelable vehicle option

    the orbital refuel just “SEEMS”, “LOOKS”, “SOUNDS” cheaper, since you (and all other supporters of this concept) ALWAYS use the “trick” to compare the price of a vehicle with its propellents launched with an EXPENDABLE rocket vs. a refuel propellent launched with REUSABLE rockets

    but, if we have a REUSABLE rocket, we can (simply) use it to launch (both) vehicle AND propellents with the SAME rocket at the SAME price (or lower) and the SAME reliability (or much higher) of a multiple launches missions (vehicle + several refuel rockets)

    about your claim that “With it, you can launch much bigger ships with already existing commercial rockets, launching them empty.” that’s true if you refer to the DIMENSIONS but NOT TRUE if we look at its TOTAL PRICE

    in other words, the bigger vehicle refueled in space may carry the SAME payload to the Moon at the SAME price of SEVERAL smaller vehicles launched FUELED form Earth, that, since (today) the “price” to launch “one ton of vehicle” OR “one to of propellent” to LEO is THE SAME

  13. Gabriel says:

    Gaetano, i’m happy you admit rockets with under 20000$/kg to LEO capacity already exist 😉 and the fact as you mentionned Space X are not the only ones to offer this sort of prices.

    No need of reusable rockets to achieve lower prices (i am a fan of reusable rockets, but we don’t even need go this way)… Industrial production in quantity of the same ELV rocket will lower its price. And a rocket tanker could be simpler/cheaper (Otrag like) than a rocket used to lift expensive satellites.

    > “that’s true if you refer to the DIMENSIONS but NOT
    > TRUE if we look at its TOTAL PRICE.”

    Total price is not all the story, the fuel depot being a reusable infrastructure would open new horizons (reusable/refuelable space tug, topping TLI stages, refueling LEO or GEO satellites with a tug…).

  14. @Gabriel

    “you admit rockets with under 20000$/kg to LEO capacity already exist”

    the SpaceX prices are just a Wal Mart offer to “launch the produvt” while the REAL price is much higher

    “no need of reusable rockets to achieve lower prices”

    true, this is also my opinion, but, if/when the prices will fall down to 1/10th, there will STILL be NO difference between the “end user price” of a fully fueled vehicle and a fueled-in-space one

    “fuel depot being a reusable infrastructure would open new horizons”

    that will be true with an Altair refueled with lunar ISRU propellents (saving the higher costs to send the propellents from Earth) while I did not see any advantages or saving for LEO operations since the price-per-kg. to LEO of “one ton hardware” or “one ton of propellents” is the same

  15. gravityloss says:

    Hey, good discussion! I was on a trip, maybe I’ll do a post on the cost vs flight rate vs rocket size issue soon.

  16. Pingback: Flexible Path for NASA Exploration « Gravity Loss

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