- 83 Views
- Uploaded on
- Presentation posted in: General

DEIMOS SPACE SOLUTION TO THE 3 rd GLOBAL TRAJECTORY OPTIMISATION COMPETITION (GTOC3)

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

DEIMOS SPACE SOLUTION

TO THE 3rd GLOBAL TRAJECTORY OPTIMISATION COMPETITION (GTOC3)

Miguel Belló, Juan L. Cano

Mariano Sánchez, Francesco Cacciatore

DEIMOS Space S.L., Spain

- Problem statement
- DEIMOS Space team
- Asteroid family analysis
- Solution steps:
- Step 0: Asteroid Database Pruning
- Step 1: Ballistic Global Search
- Step 2a: Gradient Restoration Optimisation
- Step 2b: Local Direct Optimisation

- DEIMOS solution presentation
- Conclusions

- Escape from Earth, rendezvous with 3 asteroids and rendezvous with Earth
- Depature velocity below 0.5 km/s
- Launch between 2016 and 2025
- Total trip time less than 10 years
- Minimum stay time of 60 days at each asteroid
- Initial spacecraft mass of 2,000 kg
- Thrust of 0.15 N and Isp of 3,000 s
- Only Earth GAMs allowed (Rmin = 6,871 km)
- Minimise following cost function:

- Miguel Belló Mora, Managing Director of DEIMOS Space, in charge of the systematic analysis of ballistic solutions and the reduction to low-thrust solutions by means of the gradient-restoration algorithm
- Juan L. Cano, Senior Engineer, has been in charge of the low-thrust analysis of solution trajectories making use of a local optimiser (direct method implementation)
- Francesco Cacciatore, Junior Engineer, has been in charge of the analysis of preliminary low-thrust solutions by means of a shape function optimiser
- Mariano Sánchez, Head of Mission Analysis Section, has provided support in a number of issues

- Semi-major axis range: [0.9 AU-1.1 AU]
- Eccentricity range: [0.0-0.9]
- Inclination range: [0º-10º]
- Solution makes use of low eccentricity, low inclination asteroids

- To reduce the size of the problem, a preliminary analysis of earth-asteroid transfer propellant need is done by defining a “distance” between two orbits
- This distance is defined as the minimum Delta-V to transfer between Earth and the asteroid orbits
- By selecting all asteroids with “distance” to the Earth bellow 2.5 km/s, we get the following list of candidates:
- 5, 11, 16, 19, 27, 30, 37, 49, 61, 64, 66, 76, 85, 88, 96, 111, 114, 122 & 129

- In this way, the initial list of 140 asteroids is reduced down to 19
- Among them numbers 37, 49, 76, 85, 88 and 96 shall be the most promising candidates

- The first step was based on a Ballistic Scanning Process between two bodies (including Earth swingbys) and saving them into databases of solutions
- Assumptions:
- Ballistic transfers
- Use of powered swingbys
- Compliance with the problem constrains

- This process was repeated for all the possible phases
- As solution space quickly grew to immense numbers, some filtering techniques were used to reduce the space
- The scanning procedure used the following search values:
- Sequence of asteroids to visit
- Event dates for the visits

- An effective Lambert solver was used to provide the ballistic solutions between two bodies

- Due to the limited time to solve the problem, only transfer options with the scheme were tested:
E-E–A1–E–E–A2–E–E–A3–E–E

- All possible options with that profile were investigated, including Earth singular transfers of 180º and 360º
- The optimum sequence found is:
E–49–E–E–37–85–E–E

- Cost function in this case is: J = 0.8708
- This step provided the clues to the best families of solutions

- A tool to translate the best ballistic solutions into low-thrust solutions was used
- A further assumption was to use prescribed thrust-coast sequences and fixed event times
- The solutions were transcribed to this formulation and solved for a number of promising cases
- Optimum thrust directions and event times were obtained in this step
- A Local Direct Optimisation Tool was used to validate the solution obtained

- Final spacecraft mass: 1716.739 kg
- Stay time at asteroids: 135.2 / 60.0 / 300.3 days
- Minimum stay time at asteroid: 60 days
- Cost function
- Solution structure:
- Mission covers the 10 years of allowed duration
- Losses from ballistic case account to a 0.05%

E – TCT – 49 – TC – E – C – E – TCT – 37 – TCT – 85 – TC – E – CTCT – E

Segment Earth to asteroid 49:

- E–TCT–49
- 2½ revolutions about Sun
- Duration of 1,047 days

- Segment asteroid 49 to 37:
- 49-TC-E-C-E-TCT-37
- 2½ revolutions about Sun
- Duration of 852 days

Segment asteroid 37 to 85:

- 37–TCT–85
- 1¼ revolutions about Sun
- Duration of 450 days

- Segment asteroid 85 to Earth:
- 85–TC–E–CTCT–E
- 2½ revolutions about Sun
- Duration of 836 days

- Use of ballistic search algorithms seem to be still applicable to provide good initial guesses to low-thrust trajectories even in these type of problems
- Such approach saves a lot of computational time by avoiding the use of other implementations with larger complexity (e.g. shape-based functions)
- Transcription of ballistic into low-thrust trajectories by using a GR algorithm has shown to be very efficient
- Failure to find a better solution is due to:
- The a priori imposed limit in the number of Earth swingbys (best solution shows up to 3 Earth-GAMs)
- Non-optimality of the assumed thrust-coast structures between phases