Table 1 Objectives and requirements for visibility calculations
From: Visibility analysis of Phobos to support a science and exploration platform
Objective | Requirement | Justification | Data |
|---|---|---|---|
Remote sensing of the Mars atmosphere and surface | Visibility of Mars > 0 min | Visibility of Mars dayside and nightside | No map required due to Phobos’ tidal lock and equatorial orbit. All Mars local times are covered equally. Dayside and nightside are both observed ~ 3 h 50 min per orbit |
Visibility from Deimos during Mars occultation | If stations are located on both Phobos and Deimos, attenuation of a signal transmitted between the two captures information about Mars’ atmosphere and ionosphere | Map of Phobos quantifying the number of occultation events showing locations where the line of sight to Deimos intersects Mars’ surface | |
Radio/ranging science: Geodesy, dynamics, gravity, fundamental physics | Visibility from Deimos: ≥ 2 h per day | Both cases are mostly covered by the GPS requirement | Boolean map of Phobos true where visibility from Deimos is ≥ 2 h per day |
Visibility (laser ranging) from Earth ≥ 2 h per day | Boolean map of Phobos true where visibility from Earth is ≥ 2 h per day | ||
Phobos in-situ science | No requirements | All locations on Phobos have science potential | - |
Mars space environment monitoring | Visibility from Sun (solar wind) 2 h per day | Solar wind monitoring | Boolean map of Phobos true where solar visibility ≥ 2 h per day |
Data relay | Visibility from Earth ≥ 6 h per day, except during solar superior conjunction | 6 h is considered a basic requirement (including consideration of eclipses) for ESA planetary missions | Boolean map of Phobos true where Earth to Phobos visibility ≥ 6 h/day |
Visibility from Mars > 0 min Minimum elevation angle (above horizon) = 10° | Link to surface rover for data downlink or telecommanding. As an example, we use the NASA Mars Science Laboratory landing site at Gale crater: 5.4°S, 137.8°E | Boolean map of Phobos true where a rover landing site to Phobos visibility > 0 min/day (accounting for a buffer in elevation of + 10° above horizon) | |
Visibility from Jupiter: at least 3 h per day, during solar superior conjunction (Earth-Jupiter) | 3 h per day is estimated to provide sufficient data volume for downlink of housekeeping data and uplink of telecommands from and to the JUICE spacecraft | Boolean map of Phobos true where Jupiter to Phobos visibility ≥ 3 h, there is a solar superior conjunction | |
Global Mars positioning system | Visibility from Deimos ≥ 2 h per day | For positioning, laser ranging, radio tracking | Boolean map of Phobos true where Deimos to Phobos visibility ≥ 2 h per day |
Visibility to Phobos from Mars and Deimos simultaneously | Concurrent visibility of Phobos and Deimos from the surface of Mars allows better positioning | Map of Mars showing hours per day where Phobos and Deimos are concurrently visible | |
Power (assuming solar power system) | Solar illumination should be ≥ 4.5 h per day | This time duration is estimated based on previous studies (ESA Concurrent Design Facility Study Report: Phobos Sample Return 2014) | Boolean map of Phobos true where visibility from Sun is ≥ 4.5 h per day |
Public outreach | Visibility from Mars: once per day on the dayside of Mars | Public outreach ‘Phobos-webcam’ | Visualisation to demonstrate outreach potential |