Thread: Mars physics

Hello, I was reading that NASA was testing a craft that could land on Mars and the article mentioned that since there's no water on Mars the craft can't land gently in it. As I was reading I wondered, can't we invent a device that could carry a certain amount of water to be deployed before we land? We can look at Mars and measure the radius of a crater and the profundity as well. Of course if it takes millions of dollars on fuel just to depart from Earth, carry water to Mars could be consider pointless and unecessary. But if we manage to make a little landing zone where crafts can land gently it would be better right? What do you think of my idea?

Also I was wondering, what happens to water on Mars? If we take for example a galon of water and we leave it on Mars, in how many time it will evaporate?

Thank you for your time.

Parachutes, or an aerodynamic landing, will make a soft landing possible ¹.
As for water - apart from the fact it would would freeze or evaporate (and it would probably be a race as to which happened first) - how much water do you think would be needed to give a soft landing? We'd have to take enough to completely fill - to the required depth - a fairly large crater.
Any water that's taken would also reduce the payload - scientific instruments etc. of the lander.Spacecraft have very strict limits on maximum weight because we have to get that mass into orbit first.

1 AFAIK ALL Russian/ Soviet spacecraft (including manned ones) land on dry land - within Russian territory - and have no problems doing so.

For the Rovers they used airbags.
Mars Exploration Rover Mission: Technology

This is how they perform a soft landing now.

Originally Posted by Dywyddyr

Parachutes, or an aerodynamic landing, will make a soft landing possible

They help a lot, but parachutes alone (or even wings) cannot bring a spacecraft to a survivable landing in Mars. The atmosphere is too thin. Hence the use of landing rockets for all Mars landing missions to date.

Originally Posted by billvon

They help a lot, but parachutes alone

NASA seems to think differently.

(or even wings) cannot bring a spacecraft to a survivable landing in Mars. The atmosphere is too thin. Hence the use of landing rockets for all Mars landing missions to date.

If wings can't bring a craft to a survivable landing I wonder why there are serious plans for Mars aircraft?

Originally Posted by Dywyddyr

NASA seems to think differently.

?? That article talked about NASA's supersonic decelerator; a parachute that can be deployed at very high speeds, and slow a vehicle from 1100mph to 175mph - which is not a safe speed to land at. Mars vehicles still need rockets to make a soft landing.

From the NASA/JPL website on the Mars Exploration Rover:
=========
Rocket assisted descent (RAD) motors Because the atmospheric density of Mars is less than 1% of Earth's, the parachute alone cannot slow down the Mars Exploration Rover enough to ensure a safe, low landing speed. The spacecraft descent is assisted by rockets that bring the spacecraft to a dead stop 10-15 meters (30-50 feet) above the Martian surface.
=========

If wings can't bring a craft to a survivable landing I wonder why there are serious plans for Mars aircraft?

Because you can drop an airplane from orbit and have it fly around pretty easily, then either crash it or land it softly via rockets.

Originally Posted by billvon

?? That article talked about NASA's supersonic decelerator; a parachute that can be deployed at very high speeds, and slow a vehicle from 1100mph to 175mph - which is not a safe speed to land at. Mars vehicles still need rockets to make a soft landing.
From the NASA/JPL website on the Mars Exploration Rover:
=========
Rocket assisted descent (RAD) motors Because the atmospheric density of Mars is less than 1% of Earth's, the parachute alone cannot slow down the Mars Exploration Rover enough to ensure a safe, low landing speed. The spacecraft descent is assisted by rockets that bring the spacecraft to a dead stop 10-15 meters (30-50 feet) above the Martian surface.
=========

The Mars Rover didn't use the LDSD.

Because you can drop an airplane from orbit and have it fly around pretty easily, then either crash it or land it softly via rockets.

Or land it "normally" THEN slow down.

Originally Posted by Dywyddyr

The Mars Rover didn't use the LDSD.

Right. It used a different parachute that also needed a rocket landing stage.

Or land it "normally" THEN slow down.

Sure, you could. But landing at well over 100mph on a rocky plain presents some technical challenges.

Originally Posted by billvon

that also needed a rocket landing stage.

Not according to the linked promo PDF.

Originally Posted by Dywyddyr

Not according to the linked promo PDF.

I looked and saw nothing that said a soft landing on Mars was possible with just a parachute. Indeed they mention this:

"Mars has a tricky environment somewhere
in-between: it has too much atmosphere to allow rockets
alone to land heavy vehicles, as is done on the moon, but
too little atmosphere to land vehicles from space purely
with friction and parachutes, as is done on Earth."

"A new parachute with a modified design, approximately 110 feet (33.5
meters) in diameter—more than twice the area of the most recent
Viking-based parachute used to land Curiosity—also will be developed
to further slow the entry vehicle from Mach 2 to subsonic speeds."

Needless to say, merely slowing down to "subsonic speeds" is insufficient to soft-land anything. You might be able to land a penetrator probe with just a parachute, but it would have to be designed to take hundreds of G's from the impact at several hundred miles per hour.

Originally Posted by billvon

I looked and saw nothing that said a soft landing on Mars was possible with just a parachute. Indeed they mention this:

And zero mention - even on the accompanying diagram - of using rockets for the final descent.

Originally Posted by Dywyddyr

And zero mention - even on the accompanying diagram - of using rockets for the final descent.

Uh . . . you realize that the diagram shows a test on EARTH, right?

Originally Posted by billvon

"A new parachute with a modified design, approximately 110 feet (33.5
meters) in diameter—more than twice the area of the most recent
Viking-based parachute used to land Curiosity—also will be developed
to further slow the entry vehicle from Mach 2 to subsonic speeds."

Needless to say, merely slowing down to "subsonic speeds" is insufficient to soft-land anything. You might be able to land a penetrator probe with just a parachute, but it would have to be designed to take hundreds of G's from the impact at several hundred miles per hour.

If a parachute big enough to work without rockets is 33.5 meters across, and presumably made of materials that give it sufficient durability to be useful, then one has to wonder how much heavier the rockets would have been?

I wonder if they could put helium bottles to inflate a balloon to let it gently glide down to the LZ. As the rover detaches from its primary ship the balloon could inflate rather fast.

Originally Posted by cosmictraveler

I wonder if they could put helium bottles to inflate a balloon to let it gently glide down to the LZ. As the rover detaches from its primary ship the balloon could inflate rather fast.

A helium balloon generates buoyancy by displacing air with a lighter gas; lift is dependent upon the mass of air displaced. On Mars a given balloon would have to be well over 100 tines the volume of a balloon on Earth to generate the same lift. It is likely that such a balloon would weigh far more than a parachute or the rockets it replaced.

Originally Posted by billvon

Originally Posted by cosmictraveler

I wonder if they could put helium bottles to inflate a balloon to let it gently glide down to the LZ. As the rover detaches from its primary ship the balloon could inflate rather fast.

A helium balloon generates buoyancy by displacing air with a lighter gas; lift is dependent upon the mass of air displaced. On Mars a given balloon would have to be well over 100 tines the volume of a balloon on Earth to generate the same lift. It is likely that such a balloon would weigh far more than a parachute or the rockets it replaced.

Thank you.