AAE 450 Spacecraft Design Fall 2003, Option 2 Aero-Gravity-Assist Vehicle for Jupiter Mission

S.P. Schneider Last modiﬁed September 2, 2003

Introduction The design problem for the Fall 2003 semester is to design an aero-gravity-assist vehicle for a mission to Jupiter. The design will be submitted in a final Design Disclosure Report, including an Executive Summary. Details of the requirements are on the following pages. Design teams will be formed during the first week of class. The project is to be a team effort. One member of each team is to be selected as Project Leader. The Project Leader is responsible for overseeing and coordinating the design effort, in addition to his or her other responsibilities. A schedule for reports will be handed out separately. The design will be submitted in a final Design Disclosure Report. The report is to be provided in electronic form, on a CD or Zip disk; two paper copies are also to be provided. No late reports will be accepted.

Summary of Requirements Gravity assist maneuvers have been used for some time in interplanetary exploration, to improve mission designs for spacecraft exploration. Aerodynamic forces may also be used during these flyby’s, to enable additional reductions in mission cost (Refs. 2 and 6). Ref. 2 outlines some missions which may benefit from aerogravity assist (AGA). The analyses computed to date generally assume a fixed L/D ratio or a fixed drag polar, independent of Reynolds number and Mach number, and do not provide any analysis of the thermal protection system requirements, the effect of the aeroshell volume and mass, and so on. Your task is to provide an improved preliminary design for an AGA mission. To provide a particular example in a tractable form, Wyatt Johnson has computed conditions for a spacecraft traveling from Earth to Jupiter via an AGA at Mars: ‘The present mission launches from Earth on 5/15/2004 with a launch V-infinity of 6.00 km/sec. The trajectory was found using STOUR, and the boundary conditions using JPL software called Quick (type ”quick” on the roger command line). A full reference for Quick is available online at http://roger.ecn.purdue.edu/~masl. I took the STOUR output, (in particular, the Earth launch date, Mars flyby date and B-plane angle), and in Quick was able to calculate the spacecraft and planet’s velocity at the Mars flyby date [to obtain the relative arrival and departure velocity], and then was able to convert these arrival conditions into state elements.’ The inbound and outbound states of the Mars encounter will thus be provided to you; the exact values depend on the nominal perapsis height selected, so several choices were computed and are available. A sample for a 20 km nominal periapsis height is given as follows, in Vinh’s variables (Ref. 4), in the frame of reference of a nonrotating inertial Mars:

1 20 km, inbound

Radius 7703.97920987248 [km] Latitude 5.79501877517897 [degree] Longitude 103.371702912840 [degree] Velocity Magnitude 11.5430828878192 [km/s] Flight Path Angle -62.2136191665622 [degree] Flight Path Azimuth 277.589790482671 [degree]

20 km, outbound

Radius 6630.87525943860 [km] Latitude 10.2682645534391 [degree] Longitude 262.209064628125 [degree] Velocity Magnitude 9.58306356082863 [km/s] Flight Path Angle 56.7463397103915 [degree] Flight Path Azimuth 263.541207334106 [degree]

The ﬂight path azimuth given here is the same as Vinh’s heading angle (ψ). A ﬁxed drag polar was used, with a maximum L/D ratio of 5. Your task is to design a vehicle to perform this AGA manuever at Mars. Assume the vehicle is carrying an unmanned spacecraft similar to Galileo (Ref. 3). Assume a spacecraft dry mass of 1300 kg (sans aeroshell and propulsion system), and assume that 1400 m/s of ∆V is needed to perform maneuvers at Mars and in interplanetary orbit (Table 3 in Ref. 3). Estimate the spacecraft volume from the Galileo literature. Contain this spacecraft in an aero shell for the Mars encounter. Although your vehicle may eventually use a non-ablating thermal protection system, consider an ablating thermal protection system, to reduce mass. Design the vehicle aeroshell shape, TPS, Mars-encounter orbital dynamics, structure, and propulsion system. Select internal components from those used in earlier systems such as Galileo. Compare your analyses to those present in the literature, and assess whether the mission appears more or less feasible than it appeared at the start of your project.

Revisions These requirements are a current best estimate of the desired capabilities. The preliminary design work may show that some of the requirements make the design unfeasible, or grossly limit the design with insufficient cause. Proposers are encouraged to discuss the requirements with Prof. Schneider. They may be encouraged to submit a written Request for Modification, giving justification for the requested change. If such a request is approved, it will be distributed to the other groups as an alternate version of the RFP.

Design Disclosure Report This report shall be organized as follows. All data are to be reported in SI units.

2 Executive Summary – 10 pages maximum (separately bound) A brief clear description of what the system is, what it can do, and how it meets requirements. It should include key performance results and design trades. Use ﬁgures, plots, etc., in conjunction with the text to eﬀectively communicate your results. Include at least one three-view drawing of your vehicle design, with the overall dimensions and the initial and dry masses. Write the Executive Summary assuming it may be the only thing an important customer/evaluator may read.

Introduction to the Design – 10 pages maximum This section should give an introduction to the design problem as a whole, and to your vehicle.

Comparison to the Conceptual Design – 10 pages maximum Compare the performance of your design to the performance contemplated during your conceptual design, and discuss the reasons for the changes in vehicle design and performance. Identify any errors you may have discovered.

Vehicle Systems and Propulsion – 30 pages maximum Detail the vehicle components and how they were determined. Show how all parts fit within the available space. Show the structural margins for major components. Provide a complete mass statement including the masses and center of gravity of all components including expendables and personnel. Provide three-view drawings, inboard profile, and plan view drawings showing the location of major components. Describe the propulsion system and propellant requirements (mass and volume). Use an existing flight-proven propulsion system rather than designing your own. Show propellant use schedule for each maneuver (e.g. boost, circularization, aeroassist phases, deorbit retro fire, etc.) If the system is used within the atmosphere during the aeroassist maneuvers, account for the effects of the atmosphere on performance. Describe the design of the propellant tanks, and indicate size, mass, and location for the orbiter engines and the attitude control thrusters. Describe the attitude control and orbital maneuvering system and show propellant requirements.

Aerogravity Assist Trajectory – 30 pages maximum Describe the maneuvers to be used. Present detailed information about typical trajecto- ries, such as the time variations of velocity, altitude, ﬂight path angle, latitude, longitude, heading angle, acceleration, and surface temperatures and TPS thicknesses at several locations on the vehicle. Ensure that the vehicle does not hit the surface (Olympus Mons may be 21 km above the mean surface level).

Aerothermodynamics – 30 pages maximum Develop an aerodynamic model for the vehicle in hypersonic flow, and determine lift, drag, and moment coefficients. For appropriate center of gravity locations, examine trim and stability in pitch. If necessary, develop empirical lift and drag coefficients for supersonic flow and provide a smooth transition from hypersonic to supersonic flight conditions. Determine if a significant portion of the overall vehicle energy is lost in the rarefied-flow viscous-interaction

3 regime, and if so implement improved models for this regime. Provide the aerodynamic heating environments for all missions.

Thermal Protection Systems – 30 pages maximum Select the TPS material and thickness. Describe the analysis method used, and show how the substructure temperatures are kept within required limits. Show temperature histories for critical components, and ablation rates and TPS thicknesses during sample missions. An ablating TPS must be considered as a design option, although a reusable system may be used if trade studies show it is more eﬃcient.

Structures and Loads – 30 pages maximum Describe the loads to be borne by the vehicle, and how these were estimated. Describe the structural design of the vehicle and the materials used.

Appendices – No page limit and separately bound Do not put any essential material in the Appendices. They should be viewed as backup data which an evaluator can consult for additional detail if desired. Extended tables should be provided electronically, in ASCII. Codes should also be provided in electronic form. A zip disk or CD-R is one good way to provide an electronic form of the ﬁnal codes and tables. Code documentation in the form of comments and references should be suﬃcient to allow the reader to use and modify the code.

General Notes Any section with more than the above specified number of pages will be judged on the contents up to the allowable number of pages. A table of contents with page numbers will be provided. A compliance matrix will also be provided: this is a cross reference of all the requirements, with the page number in the report where the requirement is shown to be satisfied. Graphs and figures do not have to be a full page. In fact, several smaller figures are often more useful than one large figure. All figures should be referred to in the text by number so that the relationship of the figures and text is clear. No text should be smaller than 1/16 inch in height. The data plotted in the figures should be provided numerically in the appendices. In all sections, describe the reasons for major design decisions. Is the design a ‘best’ or excellent one? In what ways, and why do you think so? What were the limitations on your ability to come up with the ‘best’ design? What are the most important limitations in your analyses? What are the next steps you would take if authorized (or funded) to proceed further with the design? References to other documents or other sections of your report should contain page numbers as well as document citations or section numbers. There are many references available to aid you in learning to write a good technical report. One of these, Communicating technical information; a new guide to current uses and abuses in scientific and engineering writing, by R. Rathbone, is on reserve in the Engineering Library.

4 Evaluation of the Designs Grades will be determined by Prof. Schneider based on the individual’s work, and their ability to communicate and interact in a timely manner with the other members of their team. The following factors are also of importance:

• Innovation

• Understanding of all aspects of the problem

• Technical validity

• Design completeness

• System integration

• Ability to meet requirements

• Neatness and professional presentation (without embellishments)

References

1. Kolodziej, P, Bowles, J., and Roberts, C., Optimizing hypersonic sharp body concepts from a thermal protection system perspective, AIAA Paper 98-1610, April 1998.

2. Johnson, Wyatt, Optimization of Atmospheric Flythrough for Aerogravity-Assist Tra- jctories, report for AAE 508, Optimization in Aerospace Engineering, Spring 2000.

3. O’Neil, W., Project Galileo, AIAA Paper 90-3854, Sept. 1990.

4. Tauber, M.E., J.V. Bowles, and L. Yang, Use of atmospheric braking during Mars missions, J. Spacecraft and Rockets, v. 27, no. 5, pp. 514-521, Sept.-Oct. 1990.

5. Vinh, N., Busemann, V., and Culp, R., Hypersonic and Planetary Entry Flight Me- chanics, Univ. of Michigan Press, 1980.

6. Walberg, G.P., A survey of aeroassisted orbit transfer, J. Spacecraft and Rockets, v. 22, n. 1, pp. 3-18, Jan.-Feb. 1986.