FYI,

"The Mega-Module Path To Space Exploration Or: How To Use An HLV"
OpEd by John K. Strickland, Jr.
Space Daily
http://www.spacedaily.com/news/oped-05zza.html

: Ever since the abrupt demise of the Saturn V rocket system at the
: end of the Apollo era, engineers and space advocates have dreamed
: of what they could do with a booster of similar capacity.

: The recent correct decision by Griffin and his team to go for the
: largest available booster which can be created at a reasonable
: cost, will now allow us to make big plans for the first time in
: 35 years. This article focuses on how to exploit the wide variety
: of large payloads which an truly large HLV makes possible.

: Replacing the shuttle orbiter and external tank with a second stage
: based on the ET itself will provide greatly increased flexibility
: and capability. The only capability lost is that of returning large
: payloads, and this capability has been used only a few times to
: advantage.

: The extreme annual cost of maintaining the shuttle system could
: have paid for duplicating these payloads many times over. The
: ability to launch payloads of 100 or more tons with a payload
: shroud diameter of over 27 feet far outweighs that loss. Using
: a "hammerhead" type shroud could allow payloads of at least 30 feet
: across.

: There are several obvious reasons for wanting a large booster,
: (beyond just the ability to launch a bigger payload), such as
: avoiding multiple launches and the massive complications and delays
: that would accompany them.

: However, one kind of multiple launch system deserves a second look.
: Most of the potential problems with supporting a single mission
: with multiple launches result from launch failures or delays in
: launching one or more payloads needed for a given mission. But what
: if one of the two payloads is already in space.

: A large portion of every spacecraft is propellant, and there is no
: need to launch fully-fueled vehicles if the fuel could be already
: waiting for them in orbit. Admittedly, this does call for the
: exploration vehicle to go into orbit instead of on a direct
: trajectory to the Moon or Mars and it does result in some
: disadvantages.

: However, in this case, the advantages far outweigh the
: disadvantages. Launching payloads with empty tanks would in many
: cases more than double the available launch mass of any integral
: exploration spacecraft which could be launched on a given HLV,
: allowing the spacecraft being launched to be larger.

: Every ton of propellant that does not have to be on the spacecraft
: can be replaced by an equivalent ton of useful spacecraft
: structure. It would allow post-launch checkout of all spacecraft
: systems before departure from vicinity of Earth. It would require
: temporary docking to load fuel, but no assembly of modules in
: space. The key to this tactic is the orbital fuel (or propellant)
: depot.

: Having an HLV capable of putting 100 or 120 tons in orbit enables
: us to launch a complete (but empty) fuel Depot into orbit with a
: single launch. If the Depot is capable of storing propellant for
: extended periods, the propellant itself can be delivered long
: enough in advance of mission dates to prevent any delays.

: In order to do this, the depot needs to be able to continuously
: re-liquefy propellants as they boil off using solar energy from its
: own solar panels. The Depot would have several redundant fuel and
: oxidizer tanks.

: It should be able to handle several types of fuel and oxidizer. It
: would be human-tended (operated by astronauts to put propellants in
: from a propellant-carrying launch or to take propellant out for a
: mission spacecraft.) There would be no permanent human crew needed.

: The Depot would need to be well shielded from space debris and
: thermal cycling in orbit, as well as extra insulation to reduce
: boil-off. The external surface of the Depot could also serve as
: part of the shroud.

: The depot would have a primary 3-axis attitude control system
: assisted by its shape, allowing gravity gradient forces to reduce
: the use of attitude control fuel. The large weight allowances would
: permit extra shielding, extra insulation and more redundant systems
: than a minimal version might allow. The total amount of propellant
: a depot could handle would depend primarily on the propellant's
: density, since there is no weight penalty in orbit.

: Propellants to fill the depot could be delivered using a second
: launch of the HLV. Timing for these launches would not be crucial.
: Propellants could be delivered in a lightweight tank with minimal
: insulation (similar to the existing ET), and then immediately
: transferred to the depot. The lightweight tank could then be
: discarded and set for re-entry.

: Fueling operations in orbit are in some ways safer than on the
: ground, since any vapors escaping from propellant transfer
: operations would almost instantly dissipate in the vacuum and would
: present virtually no explosive hazard. One problem that orbital
: propellant transfer operations needs to deal with is, of course,
: the behavior of liquids in micro-gravity. Transfer pumps need to be
: delivering liquids, not pockets of gas mixed in the liquids. This
: problem has been solved in the past and there are multiple ways to
: handle it.

: If an automatic propellant transfer technology could be developed,
: no on-site crew would even be required. Any such automatic system
: would depend on a docking system, which (in addition to primary
: docking), would also have to connect fuel lines, transfer the
: propellant, and then detach the connections. These operations could
: be done by using a miniature version of the primary docking system,
: except that the respective positions of pipe connections would
: already be known to within about a millimeter.

: Control of such an operation could be handled remotely by a ground
: crew using video cameras, full data readouts and manual controls
: for connections, valves and pumps. Alternately, a crew in a CEV
: could be launched with a lighter version of the tanker.

: Depending on the orbit used by the Depot, the CEV could separate
: from the tank, and then rendezvous with a space station, or could
: even be used to deliver a crew to an exploration vehicle. Fuel
: transfer technology experiments should therefor be given high
: priority for space on remaining shuttle missions to the space
: station.

: Such a large propellant depot could be described as one type of a
: Mega-module. The standard shuttle payload limit for space station
: modules is about 20 tons, so these payloads would be 5 or 6 times
: larger than that. Once one type of mega-module, such as a depot,
: has been defined and designed, it will quickly become apparent that
: it could be used in multiple locations. It then becomes obvious
: that you need to build several copies of some kinds of modules,
: such as the fuel depot.

: A depot could also be used at a transfer location, such as Lunar
: Orbit, or the Earth-Moon L1 or L2 points. A smaller version would
: be very useful on the Lunar surface if production of Lunar oxygen
: begins. A depot would even be needed in Mars orbit once extensive
: human exploration operations begin. Once you have several copies
: under construction, there is less of a problem and/or program delay
: if one copy is lost during a launch failure.

: Once you decide to design and launch one kind, the possibilities of
: creating other types of mega-modules are immediately obvious. (If
: we have a big booster, we should use it to full advantage.) Some of
: these could be components of exploration vehicles, while others
: could be part of unrelated space development (which includes
: scientific infrastructure).

: For example, a refuge module, such as would provide a safe retreat
: from the space station, or at L1, L2, or Lunar orbit, would have
: much in common with the kind of habitation module used to transit
: between earth and Mars orbit.

: It would also be much easier to design a solar storm shelter area
: in a 100 ton module than in a 20 ton module. The large available
: diameter would provide room to place the "storm cellar" in the
: middle of a variety of food and water stores. It also might be
: possible to create refuges at Depot sites, which would already have
: solar power and attitude control available.

: There are many kinds of integral structures for which it is
: difficult to design a modular version if they have to be assembled
: in space. Imagine having to design a large motor home so it can be
: re-assembled in several pieces with a small crew in a short time.

: Segmentation of structures and space vehicles causes a lowering of
: structural integrity, and requires additional horrendously
: expensive crew time to re-assemble them in space. It is also better
: for vehicles that will be subjected to thrust to be orbited as one
: piece. This also reduces the amount of potential air leakage at
: permanent seal joints of a composite structure.

: Any kind of integral re-usable vehicle tends to be larger than the
: equivalent set of expendable components. Re-entry vehicles are a
: good example of something with a minimum functional size. For
: example, a re-usable Mars orbit to surface ferry needs to enter the
: Martian atmosphere, and be large enough to reach Mars orbit after
: re-fueling on the surface.

: Such a ferry would need to have a very large integral aero-shell
: which itself could not be launched on a small vehicle due to its
: bulk. The same is true of a re-usable lunar ferry, even though it
: does not need an aero-shell. The expendable ferry can discard the
: descent stage when returning to lunar orbit or a nearby L-point.

: The re-usable ferry must carry enough fuel to lift the equivalent
: of the descent stage back into orbit. On the other hand, less
: structure is needed, since only a single module (for ascent and
: descent) is needed. Such a ferry could carry either a CEV with
: passengers or bulk cargo. For all these reasons, having a very
: large booster makes the design of fully re-usable deep-space
: vehicles much easier.

: In a similar fashion, a host of other types of mega-modules would
: practically demand to be built. For exploration purposes, lunar
: transfer vehicles are needed for people and cargo, possibly using a
: CEV as the primary crew cabin and emergency capsule. The 60 day
: report indicates that an expendable trans-lunar stage would be used
: for lunar expeditions. There is no reason why this stage could not
: be re-designed into a re-usable Cis-lunar "tug", which could return
: to LEO using aero-braking.

: A large space tug with crew cabin which could also retrieve space
: station modules or even do repair missions to Geosynchronous orbit
: would be very useful. This tug should be able to re-fuel from the
: depot. For Mars expeditions, a standard Earth orbit to Mars Orbit
: propulsion module would be needed. Such a module could also use
: fuel brought in tanks from the surface of Mars to send crews back
: towards Earth orbit.

: The use of multiple types of Mega-modules would make it easier for
: international space expeditions to cooperate, since each country
: could build one or more types of modules. Since each module type
: would be integral, and have standardized interfaces, the complexity
: of having several countries work on the same module would be
: minimized.

: Astronomers would love to be able to design a space telescope with
: a 25 foot or larger diameter mirror. Some of the incipient flagship
: space telescope missions currently delayed by cost over-runs might
: be able to save money and greatly increase their light-gathering
: capacity by being re-designed as a 100 ton instrument.

: With 100 tons, you could also place a large outer-solar-system
: probe on a very fast trajectory by using additional boost stages.
: You could also build an oversize space station module complete with
: human-sized centrifuge.

: Last but not least, the HLV makes it possible to build and test a
: full-scale collector module for a Solar Power Satellite. It would
: be uneconomical to launch enough modules for a functional Powersat
: on the proposed NASA HLV, but such a test could prove out the
: ability of the module to fully deploy its huge array of solar film.
: Such a single module, if fitted with a microwave transmitter, could
: provide power for a solar-powered tug or other heavy power demand.

: Based on advanced designs done in the late 1990's, a 100 ton
: collector module could theoretically deploy solar (photo-voltaic)
: film with a total area up to 1 square kilometer, intercepting
: 1.3 Gigawatts of sunlight, and providing about 100-150 Megawatts of
: power if the film is about 12% efficient. If this test was
: successful, it could stimulate enough business interest to create a
: really cheap, fully re-usable and privately owned large HLV.

: With that, we could build a full system of PowerSats to supply the
: Earth with pollution-free power and permanently end both the energy
: and global warming problems within a single generation.

Mark Reiff