Mars Exploration Rover Mission

JPL ^ | 1-3-04 | JPL

[bonesmccoy]

Mission Timeline: Entry, Descent, and Landing

The entry, descent, and landing (EDL) phase begins when the spacecraft reaches the Mars atmospheric entry interface point (3522.2 kilometers or about 2,113 miles from the center of Mars) and ends with the lander on the surface of Mars in a safe state.

The rovers will arrive during the latter half of the northern winter/southern summer on Mars. Rover A will land at approximately 2:00 p.m. local time on Mars (with Earth set an hour after landing), whereas Rover B will land at around 1:15 p.m. local time on Mars (with Earth set as long as two-and-a-half hours after landing). That means that both rovers will land in the Martian afternoon while the Earth is still in view, allowing the Earth to receive the landing signal if the lander is on the base petal.

Entry, descent, and landing for the Mars Exploration Rover mission is an adaptation of the Mars Pathfinder method:

An aeroshell and a parachute decelerate the lander through the Martian atmosphere.

Prior to surface impact, retro-rockets are fired to slow the lander´s speed of descent, and airbags are inflated to cushion the lander at surface impact.

After its initial impact, the lander bounces along the Martian surface until it rolls to a stop.

The airbags are then deflated and retracted, and the lander petals and rover egress aids are deployed.

Once the petals have opened, the rover deploys its solar arrays, and places the system in a safe state. Communications during entry, descent, and landing will occur through a pair of low-gain antennas, one mounted on the backshell and the other on the rover itself. About 36 ten-second radio tones will be transmitted to Earth during descent through the atmosphere, which takes approximately six minutes. These tones are coded to indicate the accomplishment of critical steps in the entry, descent,and landing timeline. [More on these tones in the communications section]

A step-by-step guide to everything that will happen will be provided prior to entry, descent, and landing.

[Phil V.]

WARNING: Do not attempt the crossed-eye method without adult supervision. It could make you go blind!

Tell ya what . . . If'n I'm doin' sumpthin that gonna make me go blind I don't want no stinking adults supervining!

[Hunble]

Look very closely at that small crater in 3D. The flat bottom implies that it has been filled in.

Knowing the amount of dust blowing around the surface of Mars, that crater's floor will be a good demonstration of this environmental aspect.

Can you imagine how exciting this mission could be, if the rover was able to drill down about 10 feet and retrieve a core sample?

That is for a future mission....

[bonesmccoy]

I created the side by sides from the publicly available "raw" images posted by JPL. Hilarious that a 100 year old stereoscope would be useful in 2004 as a scientific instrument!

[bonesmccoy]

If a common event evaporated water from the surface of Mars and caused venting/loss of gaseous H20 from the surface of the planet, then the event must have occurred many billions of years ago. The southern hemisphere has a much higher crater count than the northern latitudes. I've never really understood how an impact event would leave the southern hemisphere cratered and lead to a much less cratered northern hemisphere.

[Hunble]

Please, if you have the capability to reverse the images, could you post them?

Very few people have Red/Blue glasses as required for a Anaglyph and even fewer have an old fashion stereoscope with double lenses.

Most of us, with practice, can cross our eyes.

[Hunble]

I've never really understood how an impact event would leave the southern hemisphere cratered and lead to a much less cratered northern hemisphere.

That is one of the most important aspects of the Laser elevation data obtain in the last few years. The Northern hemisphere is at a much lower elevation relative to the equator. Very close examinations of the elevation data could be interpreted as showing a coast line.

Translation: The Northern hemisphere does not have as many craters for a rather simple reason. It was covered by an ocean.

[GeronL]

well. use the moon as an example. The side that faces away from Earth (which is kinda odd in and of itself) has a lot more craters... because the Earth and its gravitational field protect the side facing Earth from being hit as often....

Now if Mars once had a Big ol' moon in the Southern sector... and its moon was hit by a comet... (causing the asteroid field further out??).... lots of debris would have hit the southern sector.... I wonder if its possible that we will some day be able to tell if a lot of the craters came at the SAME TIME???

[Hunble]

With the Earth's Moon, there is a strong gravitational component between the two bodies.

Both sides of the Moon (along with the Earth) were bombarded with the same relative amount of debris, but the visible evidence has been eroded over time.

With the Earth, we have oceans, the atmosphere and continental plate tectonics which are constantly changing and eroding any traces of ancient bombardments.

With the Moon, the side facing the Earth was subjected to a larger tidal force. What we see today as Mares, were large lava flows upon the surface of the Moon.

Due to the gravitational attraction of the Earth, there was a much larger flow of lava on the side of the Moon facing the Earth. Although present on all faces of the Moon, the majority of the lava flows are on the side facing the Earth.

[GeronL]

...so what if present-day Mars had been a moon to some destroyed (asteroid belt... comets) planet?? another interesting idea to think about...

[Gunslingr3]

Oh, sure, better we had never discovered fire or the wheel.

Do you think government bureaucrats discovered either?

[GeronL]

more food for thought!...hhmm

[djf]

I believe right now Earth would be the morning star on Mars. Hope they give us an Earth shot before sunrise.

[bonesmccoy]

Interesting hypothesis regarding a large impact event on a previous Mars moon.

Deimos and Phobos are both unusual in that they are both circling the planet and were either captured or somehow thrown to that orbit.

Your hypothesis would suggest that the planet was showered with debris from an impact event several billion years ago. If I understand your suggestion right, you are suggesting that Mars may have originally formed with a larger moon which was, in turn, hit by a large asteroid or comet, thus showering Mars with debris.

Here's some thoughts:
1. If such a moon existed, shouldn't there be a very large impact crater on Mars where the largest pieces hit the planet?
2. If such impact occurred, the transfer in momentum and energy might be enough to alter the planet's orbit. Is that the reason Mars' orbit is tilted at such an angle compared to the rest of the inner planets?
3. Conventional thought is that the Southern Hemisphere is older than the Northern Hemisphere (based on crater count). Why wouldn't the Northern Hemisphere have similar crater counts? You would think that after the bulk of the impacts, there would be significant debris still in the orbit and that this debris would be "raining" on the northern hemisphere to the same extent as the southern hemisphere.

I thought someone had estimated the amount of debris among the known asteroids?

[bonesmccoy]

Yes, I think you are correct. If the sun is still up after the Earth sets, then the Earth must rise prior to sunrise.

We should get in touch with the JPL people and see if they can snap a shot of the Earth rising as a star over the Mars horizon.

[bonesmccoy]

Incorrect thinking.

The mare on the moon exist because the moon's rotation about it's axis matches its orbital period.

No such matching exists on Mars.

[RightWhale]

If you look at the elevation of the southern hemisphere versus the northern, it looks like half of Mars's crust is missing. Similar to the Pacific basin, which is close to half of the earth's surface. Where did the crust go? Begging the question, of course, assuming there was a uniform crust over the entire planet.