MARS LANDER DESIGNS:
Many different approaches to crewed Mars lander designs have been proposed in the past 50 years. The earliest were gliders or flying wings. More recently there have been two basic types, ballistic landers with low lift over drag (L/D) and high L/D handers within a biconic (or similar aeroshell. Several lander configurations are possible with each type. These include: Conical "headlamp" landers which can be either ballistic or biconics, where the biconic aeroshell is jettisoned after entry, cylindrical tuna can landers within biconic aeroshells, and open "coolie hat" landers where components are clustered behind a large open heat shield. These are ballistic landers and, like headlamp landers, do not experience attitude rotation. Finally there are the vertically landed biconics (VLB) and horizontally landed biconics (HLB).
Each configuration has its advantages and disadvantages. Ballistic landers are simpler to design, construct and fly, but have lower cross-range maneuverability and experience higher thermal and acceleration loads during entry. Biconics are more much more challenging to design and fly, but have lower thermal and acceleration loads. HLBs, in common with headlamp and coolie-hat designs, do not need to perform a highly dangerous attitude rotation maneuver prior to landing. Compared with the vertical landed designs, HLBs also provide much better access to equipment when on the ground. This is their most attractive feature when considered as a Mars surface habitat.
The Zubrin and NASA design reference mission (DRM 1.0) crewed Mars mission proposals have received the greatest publicity. These all feature tuna can habitats. Existing Mars Analogue Research Stations (MARS) are based on these designs. However, a diversity of less publicised designs featuring HLBs show that this also is a valid approach to crewed Mars landers. The advantages and disadvantages of this configuration needs to be compared against data from existing tuna can MARS. I believe that there is excellent technical justification for basing MARS-OZ on such a configuration.
All existing Mars Analogue Research Stations (MARS) are based on cylindrical landers consisting of two circular decks 8 m in diameter, similar to those in the various NASA Design Reference Mission (DRM) and the Zubrin Mars Direct (MD) mission architectures. These MARS are all assembled on site, a method of construction that proposes logistic challenges. A alternative to such an approach to transport the MARS on site as a unit, an approach favoured by the Mars Society Australia (MSA). Such an approach requires that the MARS be a long horizontal cylinder. Such a geometry is similar to that of a range of horizontally landed biconic spacecraft or similar designs investigated by various organisations and authors.
This paper, which is based largely on the MARS-OZ proposal document, provides a brief review of such proposals with the overall diversity of crewed mars lander designs. The purpose of this is to provide a background technical rationale to HLBs to show that such a configuration is attractive in a number of areas and is a strong contender for any future crewed Mars mission. As such it should be used as a basis for at least some MARS designs, so that its advantages and disadvantages can be evaluated against existing tuna can configurations.
A TAXONOMY FOR CREWED MARS LANDERS
A detailed examination of the merits and drawbacks of various lander designs is beyond the scope of the paper. A brief summary of their attributes is however given. The earliest studies were of winged gliders or flying wing landers. The 1953 description by von Braun and the 1956 proposal of Ley and von Braun featured gliders that landed on suitably smooth surfaces. These studies all assumed that the Martian atmosphere was about 10% of Earth’s. When Mariner 4 showed that the correct figure was actually about 1%, interest in such high lift winged landers evaporated, initially in favour of ballistic and biconic entry vehicles landers. These are of several types.
Each approach has its advantages and disadvantages. Ballistic landers are characterised by low lift over drag (L/D) ratios, whereas biconic landers have high L/D ratios. Ballistic landers are simpler to design, construct and fly, but have lower cross-range maneuverability, and experience higher thermal and acceleration loads during entry. Biconics are more much more challenging to design and fly, but have lower thermal and acceleration loads. Unlike version 1.0 and 3.0 of the DRM and the MD studies, HLBs, in common with headland and coolie-hat designs, do not need to perform a highly dangerous 180 degree attitude rotation maneuver during atmospheric flight, something required for with both in both the MD and DRM 3.0 biconic scenarios. The larger footprint of horizontal landers means they offer greater surface stability than other designs. Compared with the vertical landed designs, HLBs, because of their lower profile, provide much better access to equipment when on the ground. Not only does this simplify surface operations, it is also a major safety improvement over most many other lander designs which require long landers and hoists for crew and equipment to reach the surface. The greater in-flight maneuverability of HLBs greatly facilitates the precise landing near previously landed equipment necessary in most recent Mars mission scenarios.
HORIZONTALLY LANDING BICONICS
This paper considers four major studies featuring biconic landers. These were the 1984 Case for Mars (CfM) proposal, a series of studies by the Energia design bureau in the USSR in the 1980's (see Energia 1986, 1987 and 1989, and 1991), the 1991 International Space University mission (ISU 1991), and a 1996 proposal by Grover et al. All of these, apart for the CfM study, involved horizontally landed biconics. In the CfM study the biconics landed tail first rather than horizontally, but is mentioned here, as it was influential for some later studies that used horizontal landers.
Case for Mars Biconic Landers (1984)
This mission scenario consisted of three identical chemically fuelled craft assembled in earth orbit and then launched to Mars, each carrying a crew of five on a conjunction class mission. While in transit they docked together to form a large structure that was rotated to provide artificial gravity. On nearing Mars the crew boarded three biconic landers and aerobraked, before rotating the biconics through 90 degrees to descend beneath parachutes. Final landing is by means of retrorockets. The crew modules land near three unmanned cargo landers sent on ahead by an earlier mission. Unlike the crew modules, which remain in an upright position, the cargo modules are lowered into a horizontal position after landing. Meanwhile the main spacecraft returns to earth to be refurbished for the next mission. Once unloaded the cargo modules were dragged together and used as habitat modules. At the end of the mission the crew boarded the two stage ferry biconic modules and blasted off to rendezvous with another interplanetary ferry. On nearing earth the ferry separated into its component parts and performed and aerocapture manoeuvre into earth orbit. The crew would use the upper stages of the biconics for a more rapid return to either earth or a space station.
The CfM biconics were 20 m long, had a maximum diameter of 9 m (Figure 1), and massed 28 tonnes. There were a number of innovative aspects of the scenario, these included the biconics themselves, a major departure from previous mission proposals, extensive use of aerobreaking, the use of In Situ Propellant Production (ISPP) during later missions, and using the cargo modules to construct a Mars base. These features were influential in a number of later studies, especially the 1991 ISU mission and the Grover et al. 1996 study.
FIGURE 1 - Unloading a CfM cargo lander with a tail-sitting ferry biconic in background (CfM 1984)
The Energia Lander
The Energia design bureau studied a number of Mars missions from in the 1980's and 1990's. These were large solar electric or nuclear electric spacecraft assembled in earth orbit and carried out opposition class missions. These proposals, and the Keldysh (1989) design, all used a similar landing module. This was the Energia EA (Expeditionary Apparatus) or MPK (Marsianskovo Posadochnovo Korablya).
The EA/MPK was a cylindrical spacecraft with a conical nose, 3.8 m diameter and 13 m long (Figure 2). The spacecraft massed 60 tonnes. The primary braking engine was housed in the rear of the spacecraft. A landing engine at the belly of the cylinder would then fire to bring the spacecraft to touchdown on four landing legs. The two-man crew rode to the surface in the ascent stage contained within the cylinder. The docking hatch in the nose of the ascent stage emerged from the centre of the dorsal surface of the landing block. If difficulties arose during descent, doors would open in the spine of the cylinder and the ascent stage would blast vertically from MPK and return to orbit. The crew would descend to the surface in a cylindrical inflatable airlock tunnel that deployed from the belly of the cylinder to the surface. The conical nose contained a crew living compartment. After a week on Mars the crew would return to the orbiting mother ship. The Keldysh (1989) design was similar except that the docking port was in the nose of the landing block.
The Energia design has been very influential on subsequent biconic landers, especially the horizontal landing configuration and in the placement of the ascent stage vertically within the spacecraft. The ISU and Grover et al. (1996) lander studies were at least partly inspired by the Russian designs. The most recent use of this ascent stage configuration was by version of the NASA DRM developed by Borowski et al. (2001). The overall mission architecture also influenced that of the ISU study.
FIGURE 2 - The Energia EA MPK design docked to the 1989 Mars spacecraft (Energia 1989)
The International Space University Lander
The ISU mission was designed to be use either opposition or conjunction class orbits. An opposition class orbit was proposed for the first mission and conjunction class orbits for later missions. It consisted of a single very large solar electric spacecraft assembled in earth orbit.
There were three biconic lander designs in the mission, one being the crew lander and ascent craft (Figure 3), the second being the cargo vehicle (Figure 4), and the third the habitat lander (Figure 5). Each biconic was 23 m long and 5.5 m in diameter. The mass on landing was 70 tonnes. Each lander contained a standard crew compartment and a specialised component, consisting of a habitat, ascent/abort stage, or cargo. There were six landers in the initial mission, two ferry, two habitat, and two cargo landers. There were two ferry landers only in subsequent missions, the assumption being that subsequent missions would use infrastructure from earlier missions. Each ferry carried a crew of 4. The crew rode the ferry module to the surface in the ascent stage, giving an abort to orbit capability in an emergency. On the surface the habitat landers were to be manoeuvred together to make Mars surface base that could be added to by later missions.
The ISU mission clearly owed much to the Energia proposals and CfM missions of the 1980's. Not surprisingly several contributors to the ISU study had been part of the earlier investigations. Both Energia staff and participants of the CfM study took contributed to the ISU mission. Energia's contribution can be seen in the solar electric interplanetary ferry, the use of HLBs, and the internal ascent stages. CfM influence is most evident in the use of multiple landers and the construction of a surface base from them.
FIGURE 3 - Crew and ascent HLB in ISU (1991) study
FIGURE 4 - Cargo HLB in ISU (1991) study
FIGURE 5 - Habitat biconic in ISU (1991) study.
The Grover et al. Mission
The Grover et al. (1996) focussed largely on ISPP options but also provided some valuable discussion of two HLB mission scenarios. In each case two Energia boosters were used to send three large biconics to Mars. The biconics studied were 22 m long and had a maximum diameter of 9.1 m, and were externally very similar. Internally there were major differences, however. Lander mass was approximately 35 tonnes. Two scenarios were proposed.
In scenario I, a HLB containing the ISRU plant and cargo is launched from earth (Figure 6), accompanied by tail-sitting biconic that contains the unfuelled Mars Orbit Insertion (MOI) and the Trans Earth Insertion (TEI) stages. A tail sitting biconic vehicle is launched later and contains the crew habitat. At the end of the crew’s stay on Mars the stage and the habitat are boosted into Mars orbit where they dock before leaving for Earth. On arrival at Earth a small Earth Descent Vehicle (EDV) aerobrakes to the planet’s surface.
In Scenario II, the first two launchers consist of the surface habitat, once again a horizontally landed biconic (Figure 7) and a TEI stage that aerobrakes into Mars orbit. Unlike Scenario I, the surface habitat also contains the ascent stage. The third launch takes the crew to Mars and consists of various stages and a habitat for use between planets. The Mars Ascent Stage MAS) docks with this vehicle for the return journey, and the crew compartment doubles as an EDV. All biconics used in these scenarios have the same overall proportions and dimensions.
The influence of earlier studies included the various NASA design reference missions, round which the overall mission architecture was based, the 1984 CfM study, and the 1991 ISU study. The biconics used in this study were very similar in overall external configuration to those of the 1984 CfM. The use of HLBs and internal ascent stages owed much to the ISU and earlier Energia studies. The Grover et al. study was the first to use ISPP as integral part of the mission plan
FIGURE 6 - HLB from Scenario I of Grover et al. (1996).
FIGURE 7 - HLB from Scenario II of Grover et al (1996)
Other horizontal landers
In addition to biconics, a number of other Mars lander designs take advantage of the attractive features of the horizontal configuration. These include Borowski et al. (2001) and recent Energia studies (Energia 1999, 2000). In these missions the aeroshells (triconic in the case of the Borowski et al. design and discoidal for Energia) are discarded before landing, exposing insectile landers. The Borowski et al. mission is particularly note worthy as features the first use of horizontal landing and an Energia type ascent vehicle in a NASA DRM derived mission.
WHY SIMULATE A BICONIC LANDER?
All existing MARS are based on cylindrical landers consisting of two circular decks 8 m in diameter. Discussions during Jarntimarra-1 highlighted the logistic challenges posed by assembling MARS on site. Transporting the MARS as a single unit to the chosen site seemed more attractive logistically. Road transport laws make it much easier to carry a long but comparatively low narrow structure than a high and wide one. This has led MSA to consider building an analogue HLB.
CONCLUSIONS: A HLB FOR MARS-OZ
There are six reasons justifying selecting a HLB configuration for MARS-OZ (Figure 8). They are:
I would like to thank Frank Schubert, Larry Lemke, Carol Stoker, and Jason Hoogland who provided much useful background discussion. Finally, Jozef Michalek prepared the drawings of the modules and the artwork for MARS-OZ, without which the proposal would have been a much duller document.
FIGURE 8 - A preliminary drawing of MARS-OZ by Jo Michalek showing its distinctive HLB configuration.
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