Visiting Mars?

[Moontanman]

If we do go to Mars should we actually land on Mars or land on it's moons first? Does landing on the Martian moons first have any advantages?

[Sensei]

30 minutes ago, Moontanman said:

If we do go to Mars should we actually land on Mars or land on it's moons first? Does landing on the Martian moons first have any advantages?

Did you check how small they are? ~ 150 and 280 times smaller than the Earth's Moon..

 

 

[Moontanman]

2 minutes ago, Sensei said:

Did you check how small they are? ~ 150 and 280 times smaller than the Earth's Moon..

 

 

Yes, that is one of their advantages, you can build a base there and study Mars up close with out contaminating it. The gravity is so low you could easily use mag-lev to launch probes and they could return material for study. 

 

Besides everyone knows at least one of them is a alien spacecraft...  not really but they do have material that could be used for various purposes without actually landing on Mars... 

Edited October 7, 2019 by Moontanman

[Mordred]

Now there's an idea for a good sci-fi book mine a moon out and make it into a spacecraft with a really big engine. Lmao. Might make a new version of a Death star lol.

 I really don't see any advantage of landing on one of Mars moons as opposed to simply landing on Mars the atmosphere and gravity is low enough that you wouldn't gain much advantage.

Edited October 7, 2019 by Mordred

[Sensei]

3 minutes ago, Mordred said:

I really don't see any advantage of landing on one of Mars moons

Unless there are some interesting ores on them..

 

[Moontanman]

2 minutes ago, Mordred said:

Now there's an idea for a good sci-fi book mine a moon out and make it into a spacecraft with a really big engine. Lmao. Might make a new version of a Death star lol.

 I really don't see any advantage of landing on one of Mars moons as opposed to simply landing on Mars the atmosphere and gravity is low enough that you wouldn't gain much advantage.

The idea has been bandied about a bit. The monolith has it's supporters. 

[Raider5678]

1 hour ago, Moontanman said:

Yes, that is one of their advantages, you can build a base there and study Mars up close with out contaminating it. The gravity is so low you could easily use mag-lev to launch probes and they could return material for study. 

However landing on them would be harder. (Yes, harder.)

If you're traveling at orbital velocities, it's easier to orbit something the size of Mars then one of those extremely tiny moons.

Getting into orbit increases the Delta V required to land on them.

Additionally, Mars has an atmosphere. This means you can Areobrake in the atmosphere as you're coming in for a landing, further reducing the Delta V required to land. If Mars will bleed of 1,200 M/S Delta V with it's atmosphere, from orbit, that's 1,200 M/S Delta V(Totally made up. I have no idea how much it actually is, and I"m too lazy to google it at the moment) you no longer need to carry with you in the form of fuel.

Additionally, the gravitational issues of living on Mars will be nothing to the gravitational issues of living on one of those moons. And as bad as Mars is at deflecting radiation, those moons will be worse.

Overall, the moons are simply a harder target, and harder to establish a colony on.

[Ken Fabian]

1 hour ago, Raider5678 said:

This means you can Areobrake in the atmosphere as you're coming in for a landing, further reducing the Delta V required to land.

But if you want to retain any abort or return capability then Mars requires much more equipment and fuel than Deimos or Phobos.

As a staging base they may provide resources (eg water for cracking to H2/O2 fuel for powered descent and return) that can be useful - although I remain unconvinced that, absent the hype and fiction, Mars is a desirable let alone a viable place for colonisation and think asteroid mining and space habitats, (whilst still not viable either) make more hypothetical sense to prioritise.

As far as Mars as an object of scientific study goes remote controlled and autonomous equipment will probably continue to be more cost effective and I can see a human presence on a base orbiting Mars - or dug into one of those moons - as more achievable than any base on the planet itself. Including the capability of launching small payloads of samples from the surface to that base - which could turn out better with re-usable rockets fueled with the resources from those moons rather than attempting to do that by mining and refining on Mars.

24/7... err, 30.3/7 or 7.4/7 solar might be quite viable by siting tracking panels at or near their poles. Any base or colony on Mars will find that extended dust storms will make solar and overnight storage unviable - nuclear will probably be required.

If there is continuing interest in asteroid mining (and at least it offers the potential of a genuine economic base to build on) it seems likely to be an interest in bases/space stations for servicing them, ie there will be continuing efforts to resolve the issues that apply to Deimos or Phobos. Or conversely, solving them for Mars' moons can apply to asteroid mining elsewhere.

[Janus]

3 hours ago, Raider5678 said:

However landing on them would be harder. (Yes, harder.)

If you're traveling at orbital velocities, it's easier to orbit something the size of Mars then one of those extremely tiny moons.

Getting into orbit increases the Delta V required to land on them.

 

No.  Start with the situation of a craft that has already matched velocity with Mars at the edge of its gravitational sphere of influence ( where Mars' gravity begins to over rule that of the Sun's on determining the trajectory).  From This point the craft falls in towards Mars. To land on Mars, the total delta V needed from this point on is (roughly)equal to Mars' escape velocity at its surface: 5 km/sec.

Now let's say you want to land on Phobos.  First you need to match Phobos' orbital speed.  If you were t just let the craft continue on a purely ballistic path, when it reached Phobos orbital distance, it would be moving at( roughly) escape velocity from Mars at that distance, which is 1.414 times the orbital speed of Phobos.  Unless you are incredibly wasteful, you will plan things so that your craft passes Mars so that its velocity and Phobos velocity are in the same direction as they pass each other. This way, you only have to kill the 0.414 times Phobos orbital speed difference between the craft and Phobos to match speeds. This work out to be ~ 0.903 km/sec.  From that point, in order to land on Phobos, you only require an additional delta v of 0.011km/sec, the surface escape velocity for Phobos.   Total Dv ~ 0.914 km/sec  ( compared to the 5 km/sec needed to land on Mars. And while some of this can be dealt with by aero-braking, the total Dv is still much greater. )

The one issue with a Phobos landing in in the timing, your craft has to arrive at Phobos' orbit at the same time that Phobos is at that point.  But this isn't as big an issue as it may seem.

Let's assume that your craft arrives at the proper orbital distance when Phobos is at some other point of its orbit.  The solution to this is quite simple:  When you do your burn, you don't do the full burn you would need to match Phobos's orbital speed.  Instead, you do just enough of a burn to put yourself in a elliptical orbit, one with a longer period than Phobos,  You pick an orbit so that its period is such that when you return to that point of the orbit, Phobos is at that point of the Orbit (so for instance, if Phobos was exactly on the other side of Mars, you would put yourself in an orbit with a period of just under 12 hrs. This way, Phobos completes 1 1/2 orbits in the time it takes you to complete one.)  Once you make the rendezvous, you do the second burn to circularize the orbit. You have just split the delta V need to match orbital speed with Phobos into two burns.

Edited October 8, 2019 by Janus

[Eise]

One minute physics has a video about it:

Why It's HARD To Land on Mars

 

[Raider5678]

18 hours ago, Janus said:

No.  Start with the situation of a craft that has already matched velocity with Mars at the edge of its gravitational sphere of influence ( where Mars' gravity begins to over rule that of the Sun's on determining the trajectory).  From This point the craft falls in towards Mars. To land on Mars, the total delta V needed from this point on is (roughly)equal to Mars' escape velocity at its surface: 5 km/sec.

Now let's say you want to land on Phobos.  First you need to match Phobos' orbital speed.  If you were t just let the craft continue on a purely ballistic path, when it reached Phobos orbital distance, it would be moving at( roughly) escape velocity from Mars at that distance, which is 1.414 times the orbital speed of Phobos.  Unless you are incredibly wasteful, you will plan things so that your craft passes Mars so that its velocity and Phobos velocity are in the same direction as they pass each other. This way, you only have to kill the 0.414 times Phobos orbital speed difference between the craft and Phobos to match speeds. This work out to be ~ 0.903 km/sec.  From that point, in order to land on Phobos, you only require an additional delta v of 0.011km/sec, the surface escape velocity for Phobos.   Total Dv ~ 0.914 km/sec  ( compared to the 5 km/sec needed to land on Mars. And while some of this can be dealt with by aero-braking, the total Dv is still much greater. )

The one issue with a Phobos landing in in the timing, your craft has to arrive at Phobos' orbit at the same time that Phobos is at that point.  But this isn't as big an issue as it may seem.

Let's assume that your craft arrives at the proper orbital distance when Phobos is at some other point of its orbit.  The solution to this is quite simple:  When you do your burn, you don't do the full burn you would need to match Phobos's orbital speed.  Instead, you do just enough of a burn to put yourself in a elliptical orbit, one with a longer period than Phobos,  You pick an orbit so that its period is such that when you return to that point of the orbit, Phobos is at that point of the Orbit (so for instance, if Phobos was exactly on the other side of Mars, you would put yourself in an orbit with a period of just under 12 hrs. This way, Phobos completes 1 1/2 orbits in the time it takes you to complete one.)  Once you make the rendezvous, you do the second burn to circularize the orbit. You have just split the delta V need to match orbital speed with Phobos into two burns.

When entering into the Martian system however, you can still use areobraking to reduce your velocity in order to get a capture(extremely risky, for obvious reasons.) From there, assuming you don't have a perfectly circular orbit, your periapsis will be low enough to induce drag when you pass threw it, reducing your apoapsis. This method can be used to save most of the Delta V required to land on mars. That being said, I still don't see it getting below 2-3 km/sec DeltaV, so your point still stands.