#### Notebook

Donator
Thanks both, that should be enough for him to be getting on with!

N.

#### Enjo

##### Mostly harmless
Tutorial Publisher
Donator
Oh yeah, and as far as you might imagine, a retrograde orbit would stress the lander too much in too a short time while aerobraking, because the wind would blow straight in the lander's face. In a prograde orbit, the aerobraking proceeds along the main masses of atmosphere: there's more time to bleed off energy and it's less stressful.

#### Urwumpe

##### Not funny anymore
Donator
Oh yeah, and as far as you might imagine, a retrograde orbit would stress the lander too much in too a short time while aerobraking, because the wind would blow straight in the lander's face. In a prograde orbit, the aerobraking proceeds along the main masses of atmosphere: there's more time to bleed off energy and it's less stressful.
Sounds a bit more dramatic than it is... its just 2*241 m/s more at the equator and with 180° equatorial inclination for Mars.

#### Enjo

##### Mostly harmless
Tutorial Publisher
Donator
Then let the reasoning suffice, that it's against logic, no matter the value

#### Urwumpe

##### Not funny anymore
Donator
Then let the reasoning suffice, that it's against logic, no matter the value
Yeah, also a bit of velocity less is sure not bad. :lol: But in general, the slow rotation of Mars and its small size makes it pretty harmless in that department.

#### Longjap

##### Member
Friend of mine asked "Why don't they do the rocket firing(Mars Orbit Insertion) on the side of Mars facing Earth". I could probably confuse him and myself, anyone point me in a good explanation of why not?

Thanks, N.
I know these kind of friends, they are quite demanding at times. For example they ask me to buy dirty magazines and wrap it up for their birthday. :lol:

Mine is asking "why they don't keep a parachute attached until touchdown for security?" I can reply with probably because they don't want the parachute to fall on top of the lander, but I don't know for sure.

#### Enjo

##### Mostly harmless
Tutorial Publisher
Donator
But in general, the slow rotation of Mars and its small size makes it pretty harmless in that department.
... up to the extreme case of Venus, where the entry direction doesn't really matter, as it barely rotates.

#### Urwumpe

##### Not funny anymore
Donator
... up to the extreme case of Venus, where the entry direction doesn't really matter, as it barely rotates.
Oh yeah. And up to the other extreme of Jupiter, where the rotation speed really matters, because it is about one sixth of your entry interface velocity. And both velocities are like Jupiter. HUGE.

#### Notebook

Donator
I know these kind of friends, they are quite demanding at times. For example they ask me to buy dirty magazines and wrap it up for their birthday. :lol:

Mine is asking "why they don't keep a parachute attached until touchdown for security?" I can reply with probably because they don't want the parachute to fall on top of the lander, but I don't know for sure.
Les can buy his own magazines, knowing him he probably owns the publisher...

N.

#### Urwumpe

##### Not funny anymore
Donator
Mine is asking "why they don't keep a parachute attached until touchdown for security?" I can reply with probably because they don't want the parachute to fall on top of the lander, but I don't know for sure.
Your answer is pretty much correct. Without enough descent speed, the parachute would just collapse and fall down by gravity. Since you are slowing down against gravity, this means it falls faster than your spacecraft and will entangle it, catch fire and make your spacecraft explode...

Or at least disturb the landing radar or other sensors.

#### Ravenous

##### Donator
Donator
Mine is asking "why they don't keep a parachute attached until touchdown for security?" I can reply with probably because they don't want the parachute to fall on top of the lander, but I don't know for sure.
As well as Urwumpe's answer (correct) it's also worth mentioning that Mars has a very thin atmosphere, so the parachute descent rate is still very high. (I have no idea what, but a few hundred kph wouldn't surprise me.) So the little rockets really are needed, not just to hover and land, but to burn off a lot of speed too...

#### Notebook

Donator

Not quite Springtime For Hitler.
N.

#### Ravenous

##### Donator
Donator
Mars parachute example: for the (admittedly larger) MSL (Mars Science Laboratory, i.e. Curiosity) there's a report on the entry, descent and landing including the parachute speed:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090007730.pdf

Section 2.6 says the design was for around 100 m/s speed at 1500-2000 metres above ground level. (I don't know what the exact speeds on the day were.) I'm sure it would be a little less with the parachute in place all the way down, and perhaps a much wider parachute could be used for the final stages, but a parachute on Mars would never slow a normal cargo to a safe speed unless it was very well protected...

(EDIT: this is an example of the sort of technical data you can find for NASA projects by the way. I'd love to have seen something like this for Schiaparelli.)

#### Longjap

##### Member

Not quite Springtime For Hitler.
N.
Ok, so, has anyone checked if Opportunity is still happily rolling about? It might be that the Russians just very long range missiled the poor bugger out of jealousy. That also explain why mission control is still considering this a great success. :lol:

Edit: I'm sorry, this is a serious thread. I'll let you guys take over the speculation. I'll let myself out. (Hope my parachute works):bailout:

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#### Enjo

##### Mostly harmless
Tutorial Publisher
Donator
Article said:
Even if Schiaparelli did survive the landing, the mission’s time is already running out. Because it was chiefly meant to demonstrate landing technology rather than perform science on the surface, the lander runs solely on chemical batteries that only contain a few days’ worth of power.
So to summarize the day, ESA wanted to mainly demonstrate landing techno, but their toy #Smash-Crashed, lol

G'night.

#### Notebook

Donator
It will be interesting to see the timeline of the events. As I understand the first anomaly was early release of the parachute(wrong deliberate command, or failure of the parachute?).

Then the thrusters shut down early? Again, deliberate or failure?

Lots of stuff to investigate.

N.

#### DaveS

##### Space Shuttle Ultra Project co-developer
Donator
Beta Tester
So to summarize the day, ESA wanted to mainly demonstrate landing techno
Yes, in preparation for the ExoMars 2020 rover. The big part of ExoMars 2016 was always going to be the orbiter. ESA's own orbiter is getting up there in the years (launched 2 June 2003, MOI 25 December 2003) so a new orbiter that can perform data relay was high on the list.

#### Urwumpe

##### Not funny anymore
Donator
It will be interesting to see the timeline of the events. As I understand the first anomaly was early release of the parachute(wrong deliberate command, or failure of the parachute?).

Then the thrusters shut down early? Again, deliberate or failure?

Lots of stuff to investigate.

N.
Of course. And likely the cause is something really trivial and small. Maybe an undetected software bug, because some sensor data was different to ground test scenarios.

#### N_Molson

Donator
Yeah, so many things can go wrong during a Mars entry. A gust of wind can prevent the drogue to deploy correctly, a thruster cutting off a bit early and the thing goes in an unrecoverable spin. And all that must be managed by the probe alone, Earth is too far away for anything else than software patches. And sure, Russia/SSSR was never lucky with Mars landers !

So it seems that The Great Martian Vampire struck again. :hmm:

#### 4throck

##### Enthusiast !
As I understand the first anomaly was early release of the parachute
...
Then the thrusters shut down early?
Speculation:

If the timeline is running early for multiple events, and admitting that those events are based on sensed altitude, then the lander was lower than predicted.
Meaning it came in too fast and crashed.

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