Deimos Probe and Mining Project (s)

Introduction:

Deimos is a compellingly attractive target for a space mining project focussed on water recovery, on account of its very low albedo and good spectral match with D-Type asteroids, which are thought to be rich in water. In addition, Deimos is readily accessible, with low dvs both out from LEO and back to Earth-capture (see below). If Deimos were an independent NEA, it would be one of the very largest, and would be right at the top of the list of prime targets for a rendezvous and sample return mission. A dedicated mission would probably already have been flown, but for the fact that Mars is more alluring as a ‘science object’.

Water mining and propellant production on Deimos could feed two immediate / near-term markets, being (a) for export back into the Earth-Moon system for sale and distribution through in-orbit propellant production / depot facilities; and (b) for fuelling of Starships departing for Earth-return.

Phobos is excluded from this discussion as it is deeper in the Mars gravity well and thus significantly more difficult for access and return.

Deimos: The top image was created by Emily Lakdawalla of the Planetary Society from Viking/JPL images.)

For orientation(top image): The south pole is in the deep indentation at bottom of image, and middle of light ridge is the centre of the ‘orbit-prograde face’. Mars-pointing vector is roughly in the middle of the terminator (at right)

Deimos’ rotation is locked to Mars, like Moon’s is to Earth, and T orbit= Trot= 30.3 hrs.

The two lower images were acquired 5 hours and 35 minutes apart, and are rotated ca 45 deg wrt the top image. The sun was to the left in the left image, and to the lower right in the right image. The viewing geometry is similar in the two images, but surface features appear different due to the change in illumination.(Mars Reconnaissance Orbiter images)The view is (roughly) from Mars, ie, looking down on the sub-Mars point.

Mars data:

Mars Diam.= 3400 km; Mars u = 4.305 x 10^4 km3/sec2; equatorial inclin. = 27.6 deg to ecliptic;

Mars orbital vel = 24.14 km/s; Mars sma = 228 Mkm; Orbital period = 1.88 yrs

v-esc, surface = 5.03 km/s; v-esc, 600 km altitude orbit = 4.61 km/s

Mars-out bound dv from LEO=ca 4 km/s; arrival dv into Mars C3 = 0 isca 0.6-0.7 km/s.

Deimos data: (preferable to Phobos because higher in Mars gravity well)

Deimossize:15 x 12 x 11 km; density = 1.47 t/m3;mass =1.476 x 10^15 kg

T = 235 K(lower at the poles?);

‘g’= 0.003 m/s2; esc vel = 5.55 m/s; Deimos low (20 km radius) orbit period = ca 8 hrs;

Deimos orbit (equatorial, circular)radius= 23,460 km; Period = 30.3 hrs(synchronous);

Deimos orbital vel= 1.35 km/s, thus Mars esc vel at Deimos orbit = 1.89 km/s, thus dv toC3 = 0 is (1.89-1.35 =)0.55 km/s. Circularization from post-aerocapture elliptical orbit is 700 m/s.

To achieve Earth-transfer in sertion via impulsive departure burn in Deimos orbit therefore needs a dv of (√(0.55^2 + 0.7^2) =0.8 km/s. Actual departure dv will have to be larger to accommodate plane change, which at maximum is 27 degrees, taking dv for burn upto a max of 1.2 km/s

To depart using non-impulsive thrusting (eg, ion or Hall or plasma thruster) we assume double the dv for impulsive, ie., budget for ca. 2.4km/s.

According to this data, Deimos and Phobos are spectrally identical to D-Type asteroids. Note that Deimos is a very close match to Hektor, one of the largest Trojans. (interesting findings, sucks teeth…)

However, Phobos and Deimos are NOT direct captures from the outer asteroid belt or from the Jupiter Trojans: if they were directly captured asteroids then their orbits could not be so close to circular nor so close to equatorial.

A scenario positing tidal (inside Roche Limit) disruption during close flyby of a rubble pile asteroid, with subsequent reaggregation of that fraction of the rubble which got injected into bound orbits, is (we think) the best-fit to explaining the extremely circular and extremely equatorial nature of the orbits of Phobos and Deimos. (The precession of nodes of inclined and eccentric debris orbits would during reaccretion smear out the inclination and eccentricity of the assembling bodies.)

 

Being in Mars orbit means that most of the debris ejected via later meteorite impacton these bodies then goes into a circum-planetary torus centred on each satellite, and thus has a good chance to re-accumulate. During reaccretion, we can expect collection of solar wind volatiles, just as on the surface of the Moon. But the regolith will be not as mature as lunar regolith, as these are now thought to be relatively young bodies, and not as compacted, because of the milli-g gravity.

 

Deimos:

The images below draw attention to a possible mine site at the south pole, where there is a massive indentation and possible volatiles cold trap.

Note, however, the diggability of the regolith should be much easier than for Moon, due to the lower gravity and lower meteorite impact gardening rate. In addition, interpretation of Arecibo radar returns suggests a Deimos surface density of <1.1 t/m3 (!!).

Red vector is ‘Mars-pointing’, with Mars direction being to the upper right; blue vector is north-south; and green vector is prograde–retrograde around orbit, with prograde (leading face) being towards upper left.

(remember, everything in the solar system rotates anticlockwise, looking down from celestial north-or clockwise, looking up from celestial south.)

(this and the following images are from www.projectrho.com, aka ‘atomic rockets’ webpage, referencing Hopkins &Pratt, 2011,‘….Deimos and Phobos as Destinations for Human Exploration…’, AIAA 2011-7104.)

There are old papers in the literature (eg Fanale & Salvail) that suggest presence of ice at depth of ca 10 metres at Deimos’ poles; but they did not take into account the discovery of the south polar basin topography, which could suggest either much shallower occurrence of buried ice, or even presence of surface deposits.

There is a risk that the genesis theory of tidal disruption of a D-Type rubble pile asteroid into a circumplanetary rubble torus, followed by subsequent re-accretion, might have totally dewatered the resulting bodies. We cannot know the fact of that until ground truth is obtained.

 

On the other hand, the location of Phobos and Deimos within the irtori of slowly-regardened regolith, and the constant availability of the solar wind, suggest these bodies will be much more avid collectors of solar wind volatiles than normal asteroids in deep space. There may thus have been active collection of volatiles, potentially counterbalancing losses during disaggregation and reaccretion.

Concept level point-design for Deimos ‘Sample Return’ mission:

(confidential)

Deimos ‘Rendezvous and survey’ mission: scope:

(confidential)

Appendix:

Busch et al, Icarus, Feb 2007: Arecibo Radar Observations of Phobos & Deimos

‘In November 2005, we observed the moons of Marsusing the Arecibo 2380-MHz (13-cm) radar, obtaining a result for the OC radar albedo of Phobos (0.056) consistent with its previously reported radar albedo and implying an upper bound on its near-surface bulk density of 1.6 t/m3. We detected Deimos by radar for the first time, finding its OC radar albedo to be 0.02, implying an upper bound on its near-surface density of 1.1 t/m3, consistent with a high-porosity regolith. We briefly discuss reasons for these low radar albedos, Deimos’ being possibly the lowest of any Solar System body yet observed by radar.’

Amazingly low surface density of Deimos…“what does this mean?”