Concepts and Approaches for Mars Exploration (2012) 4315.pdf

RED DRAGON: LOW-COST ACCESS TO THE SURFACE OF MARS USING COMMERCIAL CAPA- BILITIES. J. S. Karcz1 (john.s.karcz@nasa.gov), S. M. Davis2 ([email protected]), M. J. Aftosmis1, G. A. Allen, Jr.3, N. M. Bakhtian4, A. A. Dyakonov5, K. T. Edquist5, B. J. Glass1, A. A. Gonzales1, J. L. Heldmann1, L. G. Lemke1, M. M. Marinova1,6, C. P. McKay1, C. R. Stoker1, P. D. Wooster2, K. A. Zarchi1, 1National Aeronautics and Space Adminstration (NASA) Ames Research Center, Moffett Field, CA 94035, 2Space Exploration Technologies Corporation (SpaceX), 1 Rocket Road, Hawthorne, CA 90250, 3ERC, Inc., Moffett Field, CA 94035, 4Stanford Uni- versity, Stanford, CA 94305, 5NASA Langley Research Center, Hampton, VA 23681, 6Bay Area Environmental Re- search Institute, Mountain View, CA 94043.

Introduction: We will discuss the feasibility of using a minimally-modified variant of a SpaceX Drag- on capsule as a low-cost, large-capacity, near-term, Capsule Mars lander for scientific and human-precursor mis- sions. We have been evaluating such a “Red Dragon” platform as an option for a Discovery Program mission concept. A Red Dragon lander has the potential to be low cost primarily because it would be derived from a rou- tinely-flying spacecraft. Dragon is being developed to ferry cargo and crew to and from the International Space Station (ISS). The cargo variant is currently un- Trunk dergoing test flights, which will be followed by stan- dard ISS cargo missions and, eventually, crewed flights. The human variant, unlike other Earth-return Figure 1. Cargo variant of the SpaceX Dragon space- vehicles, appears to also have most of the capabilities craft. necessary to land on Mars. In particular, it has a set of berthing hardware, would be omitted. Some upgrades high-thrust, throttleable, storable bi-propellant “Super- and modifications would be necessary, e.g. for deep- Draco” engines integrated directly into the capsule space communications and navigation, planetary pro- which are intended for launch abort and powered land- tection, and payload access to the Mars environment. ings on Earth. These thrusters suggest the possibility of The spacecraft would launch to Mars on a Falcon a parachute-free, fully-propulsive deceleration at Mars Heavy rocket. Falcon Heavy is expected to be able to from supersonic speeds to the surface. Concepts for launch more than 10 t, significantly more than Red large, human-relevant landers (see, e.g., [1]) also often Dragon's expected launch mass, to a typical Mars tra- 2 2 employ supersonic retro-propulsion; Red Dragon's en- jectory specific energy, C3 ~ 10 km / s . Dragon's ex- try, descent, and landing approach would scale to those isting propulsion system is sufficient for trajectory cor- landers. Further, SpaceX's Falcon Heavy launch vehi- rection maneuvers during cruise to Mars. cle, currently under development and expected to have Dragon's trunk (Figure 1), which contains its in- its first flight in 2013, will be capable of sending Drag- space solar arrays and radiators, would be discarded on on a trajectory to Mars. before entering Mars' atmosphere. Dragon's heat shield We will discuss our motivation for exploring a Red is designed for hyperbolic entries at Earth and would Dragon lander, the primary technical questions which be capable of withstanding the lower-speed hyperbolic determine its feasibility, and the current results of our analysis. In particular, we will examine entry, descent, and landing (EDL) in detail. We will describe the mod- ifications to Dragon necessary for interplanetary cruise, EDL, and operations on the Martian surface. The anal- ysis to date indicates that Dragon is capable of deliver- ing more than one tonne (t) of payload to sites at eleva- tions three kilometers below the Mars Orbiter Laser Altimeter (MOLA) reference, which includes sites throughout most of the northern plains and Hellas. Concept: Red Dragon would be derived from the human variant of the spacecraft. Systems unnecessary Figure 2. Artist's conception of a Red Dragon landing for a Mars lander mission, e.g. crew systems and ISS on Mars. Concepts and Approaches for Mars Exploration (2012) 4315.pdf

entries at Mars. After entering the atmosphere, the ve- ined whether Dragon's launch-abort system has suffi- hicle would decelerate through a guided, lifting trajec- cient capability to decelerate through the final phase of tory. Dragon would propulsively decelerate from su- flight using propulsion alone. personic speeds to touchdown, taking advantage of its To determine whether the capsule has sufficient high-thrust retro-propulsion system and obviating the propulsive capability, we compared the final speeds at- need to develop new parachutes or other aerodynamic tainable through unpowered aerodynamic deceleration decelerators for the vehicle. SpaceX plans to include to the propulsive capacity of the launch-abort system. legs on a version of the human variant of Dragon; Red Our analysis to date has focused on landing sites rele- Dragon would land on those legs (Figure 2), modified vant to our Discovery Program mission concept; in par- as necessary for the Mars environment. ticular, it has focused on landing at an elevation three The vehicle would have a large volume (~ 10 m3) kilometers below the MOLA reference, which address- for payload. After landing, payload could access the es much of the Northern Hemisphere. Also, for the Mars environment using certain existing pathways. The analysis so far, entries followed unguided, lift-up tra- top of the capsule, where the ISS berthing hatch would jectories. We varied entry conditions (speed, flight- otherwise be, is protected by a disposable fairing and path angle, and atmospheric density) and vehicle pa- can be opened or host a payload deck. A side bay rameters (L/D and entry mass) and found that Dragon which otherwise holds ISS mission sensors and equip- is capable of landing more than one tonne of payload ment—located near the heat shield and protected by an to our target sites for a broad range of conditions. actuated door—is another route. Payload systems could Analysis of EDL continues, including considering also access the environment through new, custom path- guided entries to increase payload capacity, continuing ways. Dragon's structure is designed to contain the high detailed examination of the supersonic-retro-propulsive forces of an Earth sea-level atmosphere; for unpressur- phase of the flight, and assessing whether a combina- ized missions, the structure can accommodate large tion of guided entry and fully-propulsive descent would doors, fairings, or other routes to the outside environ- allow improved landing accuracy compared with previ- ment. During surface operation, payload services such ous landers. Although Dragon's ballistic coefficient is as power and communications could be provided by higher than previous Mars landers, it is still less than the capsule or by the payload itself; we are exploring those suggested for future human landers. Red the range of options. Dragon's EDL approach is scalable to those vehicles, Feasibility: The primary question determining and a Red Dragon mission would advance the readi- whether it would be feasible to use Dragon as an inex- ness of supersonic retro-propulsion and other aspects pensive Mars lander is whether it can successfully en- of EDL for human missions. ter, descend, and land with little or no modification. Summary: SpaceX's Dragon capsule and Falcon Specifically, the question is whether Dragon, which Heavy rocket present the possibility of delivering large was designed for Earth reentry, can decelerate and land scientific and human precursor payloads to Mars within safely in Mars' thinner atmosphere. The efficacy of the Discovery Program's cost cap. The capsule's design aerodynamic deceleration is determined by an entry ve- already includes most of the capabilities necessary for

hicle's ballistic coefficient, β = M / Cd A, where M is Mars missions. Options exist to integrate payloads with

the mass of the vehicle, Cd is its drag coefficient, and A the vehicle and for them to access the Mars environ- is its aerodynamic reference area, as well as the vehi- ment. Current analysis indicates that entry, descent, and cle's lift-to-drag ratio, L / D. Higher ballistic coeffi- landing of the capsule at Mars is feasible, and the cap- cients correspond to higher final speeds when ap- sule's descent technique would lead on a path toward proaching the surface. After slowing as much as possi- future human-mission landers. ble aerodynamically, some other method must be used References: [1] B. G. Drake, editor (2009) Human to decelerate through the remaining speed to landing. Exploration of Mars: Design References Architecture All previous Mars landers have used supersonically-de- 5.0, NASA-SP-2009-566. [2] R. D. Braun and R. M. ployed parachutes followed by subsonic retro-propul- Manning (2007) Journal of Spacecraft and Rockets, sion for terminal descent. However, since Dragon is 44, 310–323. designed for Earth entry it has a significantly higher ballistic coefficient, β > 300 kg / m2, than previous Mars landers. Its aerodynamic characteristics are at the edge of the range for which using parachutes is current- ly considered feasible [2]. Even if parachutes were fea- sible, adopting them would require a major develop- ment and qualification effort. Instead, we have exam-