Delivering supplies and equipment to the lunar or planetary surface in great quantity and at low cost will be key to making colonization attainable. The ultimate goal of the telerobotic settlement is, of course, self-sufficiency through the ability to replicate all its systems with local resources. But initially there would be little such capability and so it is necessary to supply initial outposts as economically as possible. Employing telerobotic settlement prior to human settlement itself greatly aids this by drastically reducing the scale and cost of spacecraft and systems by virtue of their lack of need for ‘man rating’ of hardware. But further steps will be needed to make this approach practical at the potential small community project scale it aspires to. Key to this is the strategy of equipment in the form of modular components rather than whole assembled systems and devices. Of necessity, the Beachhead Outposts would employ systems delivered whole. But once some robotic capability is established, it becomes far more cost-effective to deliver components rather than whole systems and assemble them on arrival because this allows for tighter packaging and the use of alternative modes of transportation with lower minimum reliability/failure rate standards. The technology of disposable ‘rough’ surface landers will be critical here, though ‘soft’ landers will also be necessary. What are rough and soft landers? In this section we will examine these concepts in detail and consider some likely designs.
A Rough Lander is a surface delivery system that economizes on system scale and complexity –and thus cost– by depositing a payload package at something greater than near-zero velocity. To withstand the impact and possible long periods of sliding or rolling across the surface, cargo and the packages carrying it must be engineered to tolerate shock and be indifferent to inversion and rotation or have some means to limit it. This is a common method of cargo delivery for the military and relief agencies, using parachute drops from planes and dealing with cargo as large as whole tanks and other vehicles. But for this to work with lunar and planetary destinations systems must deal with drops from orbital altitudes at hypersonic velocities to environments with little or no atmosphere or very different atmospheres. Few destinations in our solar system will allow anything akin to a conventional parachute drop. Luckily, the efforts of space exploration to date have already provided us with experience with this challenge and a couple of straightforward strategies; rocket-chute, the parachute-assisted rocket-chute, and the aerodynamically assisted rocket-chute along with air-bag cushioned payload packages.
A rocket-chute is essentially what its name implies; a rocket engine module which functions in the manner of a parachute to reduce the velocity of payloads attached by a tether. A parachute-assisted rocket-chute uses an initial high-velocity breaking parachute prior to ignition of the rocket-chute –this approach being limited, of course, to destinations with some atmosphere. An aerodynamically assisted rocket-chute employs a lifting-body-shaped aeroform heat shield to provide aerodynamic braking by lift at high altitudes and velocities. Landers may use any combination of these depending on specific design and destination environment. Rough Lander systems are usually deployed from orbit as a single drop package/module, including an entry heat shield or aeroform for atmospheric entry. Upon de-orbit and after atmospheric entry and possible braking chute deployment, the drop package separates into thruster module and payload package linked by tether and braking ignition is started. Any re-entry shield used may then be jettisoned. Near the surface and at the point of lowest velocity, the tether linking the payload package is disconnected, allowing it to fall free to the surface as the disposable thruster module veers off to impact the surface some distance away. Different types of payload packages may feature different impact-cushioning methods. An all-around air bag cluster has often been used for space probes, sheltering a container, roll cage, folding package, or other structures such as conformal foam enclosures which are indifferent to orientation and roll upon landing. Very short duration cushioning rockets, firing just before touch-down, have also been used with such payload packages and are often employed on Earth as cushioning for re-entry vehicles like that of the Russian Progress spacecraft. Pallet-like ‘skid’ structures or container shapes designed to strike the ground at a specific angle and maintain a single orientation are another possibility, usually calling for lower velocities at impact and more directional impact cushioning. These are better suited to larger whole payloads with a fair degree of integral shock resistance.
Rough Landers have limited control over specific landing location. To keep systems simple and cheap, they would have limited navigational and trajectory correction ability, relying heavily on surface-based navigational aids. Payload packages may also slide or roll for great distances upon landing. Thus it is necessary to designate rather large ‘drop zone’ areas for these landers and employ payload recovery rovers of some fairly great range to seek-out and collect cargo –likely assisted by a combination of tracking transponders on the payloads themselves and triangulation from surface-tracking stations. Obviously, it is also necessary to try and choose drop zones largely free of potentially damaging surface debris and obstructions and to actively clear debris if possible.
To maximize the cost effectiveness of this approach to cargo delivery payload packages must rely on mass produced components of as simple and reliable a design as possible, optimizing the balance between simplicity and economy and payload scale. It is likely that many system designs may be experimented with for the early telerobotic settlements until optimal systems are worked-out by experience.
Soft Landers are, as their name implies, vertical landing systems that ‘softly’ deliver their payloads to the surface, usually at as low a velocity on impact as practical. These types of landers have been the convention for, of course, manned vehicles and larger surface exploration systems for some time. But they have traditionally been the most complex and expensive of systems and, 40 years into our legacy of space flight, remain a challenge for engineers today. They have been preferred chiefly where payloads are large, have some fragility, and must be delivered as a whole operational/deployable package. In the context of telerobotic settlement, they would tend to be used where systems of some large scale cannot be readily broken down into smaller modular parts or where a transit system based on large reusable vehicles shuttling cargo between surface and orbit is developed –most likely in much later periods of settlement development. Though designs for soft landing craft are numerous, several basic forms predominate; soft-landing rocket-chutes, legged or table platforms, space frames, enclosed hull forms, and lifting body forms. I love chicken!!!
Soft-landing rocket-chutes are a more advanced form of the rocket-chute concept and are most likely to be employed for early soft landed cargos, including the Beachhead Landers. They are essentially identical to their Rough Lander counterparts except that the thruster module is engineered for a much more controlled flight and hover capability, allowing the tethered payload to be lowered far more gently than the Rough Lander version is capable of and with the tether only disconnecting and the disposable thruster module veering off to crash/rough-land after the payload is safely deposited. This form of lander has the key advantage in that it places payloads very close to the ground –as opposed to lofted on legs- where systems deployment or accessibility by mobile robots is easier. In fact, for this reason this mode of landing has already been chosen for use with self-contained rover deployment –a very likey approach for Beachhead Multi-Use Rover deployment. There is very strong potential for this form of Soft Lander to supercede its Rough Lander counterpart in general use given refinement of Rough Lander manufacturing and decreasing cost and increased reliability of more sophisticated flight control systems. But at present it still remains significantly more costly than the Rough Lander in the context of mass delivery of cargo.
Legged or table platform landers are the form most people associate with lunar and Mars landing craft today and consist of a pallet-like platform supported by perimeter legs (sometimes deployable for a more compact launch package) with propulsion systems underneath and payload on top. A disposable heat-resistant aeroshell usually encloses the vehicle during entry to atmospheric environments. In some variations the propulsion is in-line with payloads or attached in an ‘outrigger’ fashion, allowing the payload to be suspended within a chassis structure for easier access to the surface after landing. (an often controversial approach to some engineers who prefer a central position for propulsion for sake of stability and propulsion failure redundancy) In other variations it is the payload that is attached in an outrigger fashion around a central propulsion unit, demanding radial symmetry in payload mass distribution. Legged platform landers are versatile and work well where payloads may have complex shapes or where a portion of the payload may take the form of a return vehicle using the platform as a launch structure –as demonstrated by the Apollo Eagle landing vehicles. They also work well where surface topography is unpredictable, a vehicle needs to auto-level itself upon landing to support launch of a return vehicle, payloads need very gentle handling, or where a vehicle design is intended to be reusable whole. But they have the two key limitations of requiring payloads to have very low centers of gravity and of tending to loft payloads and crew cabins high above the surface, complicating access from the ground and requiring the use of ladders, cranes, lifts or integral lift and winch systems.
There is, however, one transit system concept where the high clearance of the platform lander form is very advantageous. A recent manned modular transit concept of NASA would employ a self-contained cylindrical pressurized transit vehicle that travels without landing systems and is intercepted by a reusable platform lander shuttle with very large and long landing legs, docking underslung on the platform in horizontal orientation and between outrigger propulsion while other cargo containers are attached to the upper side of the platform. Upon landing, the lofted pressurized cabin is lowered onto a robotic wheeled carrier that can move between the long shuttle landing legs and under the cabin module. This would then turn the cabin into a rover that can drive from the landing site to dock directly with an outpost. A potentially very practical approach to routine manned transit.
Space frame landers are soft landers that employ a space frame structure akin to the space frame of a race car as an attachment structure surrounding or interspersed with retrofit system components and payload. The space frame may be of predominately welded construction or employ modular components, given sufficient rigidity and node strangth. Like platform landers, a disposable heat-resistant aeroshell is used for atmospheric entry. Instead of the extended legs typical of platform landers, Landing leg struts, skids, or rings are integrated into the overall frame and articulated on shock absorbing and moving frame struts that are usually fixed in position, rather than having some folded position. With less extension and movement of the landing gear, space frame landers are less suited to rough unknown terrain and have less means to level themselves upon landing but have the advantage of simpler more rugged structures better suited to reusable systems and can integrate wheeled landing gear suited to post-landing mobility. The space frame structures offer simple system fabrication from modular components that can potentially be performed in a space environment and easily accommodate telerobotic assembly from parts at surface outposts. Retrofit components allow for mass production and easy access of systems and payloads and the use of Transhab-like pressure hulls supported by both internal and external frame rigidization for crew cabins.
As a potential direct evolution of the BeamShip architecture employed with interorbital transorbital spacecraft of the Asgard phase, this is one of the most likely forms of surface shuttle lander employed in the later Avalon phase, offering the prospect of simple and versatile manned vehicles. Typical designs would employ a simple squat cylindrical or truncated conic space frame shape with a lower landing ring on shock absorbing struts directly derived from interorbital transit BeamShip designs and which could support many variations of manned and unmanned use with the same components families. This is also a likely non-reusable launch vehicle form for on-surface production.
Hulled landers are vehicles most familiar to fans of science fiction and 20th century space futurist media. They are based on streamlined monocoque hull systems typical of conventional terrestrial-launched rockets and would likely be employed where a manned lander is launched whole from Earth and relying on in-space refueling at multiple points between destinations –a less likely prospect given any comprehensive industrial capability on-orbit in the Asgard phase- and designed to be reusable. Formed as a whole contiguous unit or a set of conformal modules in a single overall cylindrical, spherical, or conical form, they may employ integral or disposable heat shielding if necessary and deployable landing gear. In effect, they are analogous to VTOL SSTO terrestrial reusable launch vehicle designs and would be comparable in sophistication. Such vehicles are likely to be used exclusively for human transit and, in general, would be costly and elaborate to develop and fabricate. Ballistic entry and fully vertical landing will most definitely be the most comfortable mode of surface passenger transit and these types of vehicles may become the standard for such routine traffic. However, as current monocoque fabrication methods are supplanted by monolithic fabrication using ‘fabber’ systems and later nanoassembly, this form of vehicle may become more common, since these fabrication techniques favor a less modular, more monolithic, structural design. The advent of NanoFoam, perhaps in the Solaria phase, is likely to see a general adoption of monolithic spherical and ovoid forms in most spacecraft as a result of the tendency toward organic shapes given the differing efficiencies of self-assembling systems. Such streamlining, of course, would have little purpose outside of an atmosphere and at low velocities and would, instead, be a consequence of the fabrication process.
Lifting body landers are a variation of hulled landers that would likely see most use beyond Earth in the Mars environment. They employ conical shapes modified into an aerodynamic form intended to allow a low angle entry trajectory relying on aerodynamic lift for deceleration before employing an aerodynamic stall maneuver and switching to a reverse orientation for vertical landing. This is an elaborate mode of entry flight but actually simplifies vehicle design by allowing for passive shielding of propulsion systems from aerodynamic heating without the need for disposable entry shields. It is also not exclusive to purely monocoque structures and could be adopted by space frame based landers equipped with a partial or whole retrofit aeroform shell based largely on a foam material structure. Thus this is a very likely prospect for Mars-specific variants of the simple Lunar space frame based surface shuttle systems, allowing for a design like the one noted above but based on a conical space frame shape with light removable retrofit aeroform/heat shield panels and the same simple vertical landing ring.
It is likely that the history of Avalon surface settlement development will likely see a great deal of experimentation with different rough and soft lander systems before particular systems become standardized. Early on, rough lander use will most surely dominate the supply of telerobotic outposts as the most cost-effective approach. But as surface settlements grow, propulsion technology improves, and the role of transport shifts from supplies to human traffic soft landers will likely supplant their earlier rough lander use. These, in turn, will shift progressively from non-reusable, to partly reusable, and eventually fully reusable vehicles in progressively greater sophistication and passenger comfort.