[X] My Assistant

[paxdan]

The rovers separated from their cruise stages about 15 minutes before atmospheric entry, they would have been doing 5.4 km/s at the point they slammed into the atmosphere. How much of the 193 kg of the cruise stage would have survived passage through the atmosphere, how fast would it have been going when it impacted the surface and has anyone identified the impact location or have an image of the crater. I'm posting this in the Oppy thread as we visited Oppy's 78 kg heatshield impact site but impact location calculations and imaging of Spirits cruise stage impact site would be most welcome.

[djellison]

No - the cruise stage is totally dead once it's seperated, it cant do any sort of deflection burn.

It'll either be uprange a bit, or downrange a bit - depending on it's relative deceleration and profile thru the atmosphere compared to the nominal EDL sequence of the rest of the spacecraft.

Part of me thinks that it's fairly large and comparatively light - so it would slow down quite quickly - but then perhaps the fuel tanks would seperate from it and go further down-range. Frankly - I have no idea

Doug

[dvandorn]

No - the cruise stage is totally dead once it's seperated, it cant do any sort of deflection burn.

It'll either be uprange a bit, or downrange a bit - depending on it's relative deceleration and profile thru the atmosphere compared to the nominal EDL sequence of the rest of the spacecraft.

Part of me thinks that it's fairly large and comparatively light - so it would slow down quite quickly - but then perhaps the fuel tanks would seperate from it and go further down-range.  Frankly - I have no idea

Doug

The cruise stage, not being particularly aerodynamic, would have broken up into a lot of pieces at max deceleration. How far the individual pieces travel depends on their ratio of mass vs. drag.

The least massive pieces with the greatest surface area would have burned up, contributing a little metal to the global aerosol dust. Beyond a certain threshhold of this ratio (not necessarily the lightest or heaviest pieces, just beyond a certain point in the mass/drag ratio), a piece will survive max heating and reach the ground.

Since each piece has a different mass/drag ratio, and since that ratio changes dynamically as the air thickens, speed slows and material ablates, the pieces all separate and form a debris footprint. That footprint will almost always fall *short* of a protected entry body (like the heatshield-protected capsule) because, in the process of breaking up, the total mass of the unprotected body (in this case, the cruise stage) suddenly presents tens of times more surface area to the atmosphere it's ramming into than the single, unified body had presented. So the mass/drag ratio shifts dramatically towards the drag side of the equation, and all of the individual pieces fall uprange of the protected capsule.

Now, if the stage contained a nice cylindrical fuel tank that was both relatively massive (representing a fair fraction of the total mass of the stage), and that tank were made of a heat-resistant metal like beryllium, the tank (being a nice aerodynamic shape) would fly on to the farthest downrange end of the debris footprint. But even so, its mass/drag ratio profile would still probably have it falling uprange of the landing site.

-the other Doug