Red Dragon Discussion Thread (2)

[sdsds]

In the context of Red Dragon there will be no possibility of "waving off" the first landing attempt: direct entry is a given; whatever conditions exist (atmospheric, surface or vehicular) at the time of Mars approach are the conditions under which landing must be attempted.

Is it fair to ask whether that particular landing paradigm is really the one SpaceX wants to develop and use in perpetuity? Loss of Mission because a low probability condition occurred is a risk that robotic missions can carry. Human spaceflight missions will have a more difficult time with a landing paradigm like that.

The solution (ISTM) will be to develop with robotic precursor missions a paradigm for Mars approach and landing that allows for the possibility that adverse conditions might temporarily exist at the time of first approach. A paradigm that allows for a second chance a few days later could not only save a mission but also save the lives of crew!

Clearly I am suggesting SpaceX could attempt aerocapture followed by subsequent aerobraking and landing.

Connecting the dots: that allows for the terrain relative navigation option.

[Dalhousie]

In the context of Red Dragon there will be no possibility of "waving off" the first landing attempt: direct entry is a given; whatever conditions exist (atmospheric, surface or vehicular) at the time of Mars approach are the conditions under which landing must be attempted.

Is it fair to ask whether that particular landing paradigm is really the one SpaceX wants to develop and use in perpetuity? Loss of Mission because a low probability condition occurred is a risk that robotic missions can carry. Human spaceflight missions will have a more difficult time with a landing paradigm like that.

The solution (ISTM) will be to develop with robotic precursor missions a paradigm for Mars approach and landing that allows for the possibility that adverse conditions might temporarily exist at the time of first approach. A paradigm that allows for a second chance a few days later could not only save a mission but also save the lives of crew!

Clearly I am suggesting SpaceX could attempt aerocapture followed by subsequent aerobraking and landing.

Connecting the dots: that allows for the terrain relative navigation option.

With the change of a dust storm it could take weeks or months to clear.  Once Dragon's it's dropped the service module it will have only a few hours before it runs out of power.

I guess aerobraking with the panels still attached is possibility

[sdsds]

With the change of a dust storm it could take weeks or months to clear.  Once Dragon's it's dropped the service module it will have only a few hours before it runs out of power.

I guess aerobraking with the panels still attached is possibility

Good points! I'm dubious about aerobraking with panels attached and thus think the Dragon design isn't likely to go forward as the Mars landing design of choice.

For Red Dragon I would want them to have a sensor-guided navigation landing mode and a backup inertial-guided mode as well. I'd want that regardless of whether the sensor-guided mode was using Martian GPS or optical terrain-relative navigation.

[Dalhousie]

With the change of a dust storm it could take weeks or months to clear.  Once Dragon's it's dropped the service module it will have only a few hours before it runs out of power.

I guess aerobraking with the panels still attached is possibility

Good points! I'm dubious about aerobraking with panels attached and thus think the Dragon design isn't likely to go forward as the Mars landing design of choice.

For Red Dragon I would want them to have a sensor-guided navigation landing mode and a backup inertial-guided mode as well. I'd want that regardless of whether the sensor-guided mode was using Martian GPS or optical terrain-relative navigation.

Sounds good. Even with the option o higher previous,the landing ellipse and this landing site choice will be defined by the lower accuracy methods.

[Semmel]

In space navigation can be done with x-ray pulsars down to +- 5km. See https://arxiv.org/abs/1305.4842v1. 5km radius is quite a lot, given the precision that is required but the 5 km is just for one observation / measurement if I understand correctly. The flight profile of Dragon will be very predictable and I am sure with a stream of measurements, the in-space position can be done much better than 5 km.

[redliox]

Cross-posting as shows some on-going Red Dragon work, although discussion of landing site specifics probably best in original landing site thread:

Paul Wooster, SpaceX, on Mars landing site selection: looking at sites at latitudes < 40˚, elevation as low as possible. #LPSC2017

https://twitter.com/jeff_foust/status/843229275025227777

Wooster: identified several candidate sites, but many likely too rocky. Arcadia region looks promising. #LPSC2017

https://twitter.com/jeff_foust/status/843229571642286081

Edit: from context I think he's talking about Red Dragon landing site

There's no paper by Wooster listed at LPSC which starts tomorrow.  Some sort of pre-conference event?

Arcadia is about as flat as they come, would looking like the Viking 2 landing site but perhaps less rocky (there is no medium sized crater nearby). Very boring, but probably with shallow subsurface ice.

So SpaceX is looking for something in a flat region as high up as 40˚?  If the priority is ice that might mean they would be seeking out sites in the mid-latitudes, since the equator lacks permafrost.  However, given this is the first flight, they might just be prioritizing something flat-n-safe, not necessarily flat-n-icy.  Arcadia or Utopia or Meridani could all suffice.  Nice to get an update, although it is still teasingly vague.

[Kaputnik]

My thoughts on this:
There are two types of landing accuracy. The first, and most obvious, is the ability to land as close as possible to the target. But the second is to land somewhere within the ellipse but with the ability to avoid localised hazards. This requires some form on onboard decision making capability but for a mission like RD where the only requirement is get down on the ground safely, it is a far more important consideration.

A second point: global dust storms do not appear ovenight. Why not adpot a mission plan whereby the primary landing site is accessible safely using terrain imaging software, but have a more boring backup site that can be reached using inertial guidance only, and which would require a small correction burn a day or so before entry to change the target. That way you can plan for the worst case but still aim for something better.

[notsorandom]

The SHARAD radar on MRO indicates potential ice deposits in Arcadia a few meters below the surface. They might be too deep for Red Dragon to drill down to but there are ways it could confirm the ice is there without having to do so.

[guckyfan]

How much do duststorms obscure sight really? How low would a lander need to go before getting sight of the terrain? This should be known from observations by the rovers. In the worst of the worst dust storms or with sufficiently high probability to ignore the risk?

[Dalhousie]

The SHARAD radar on MRO indicates potential ice deposits in Arcadia a few meters below the surface. They might be too deep for Red Dragon to drill down to but there are ways it could confirm the ice is there without having to do so.

Meteorite impacts have exposed ice at ~1 m depths at this sort of latitude as I understand.

[redliox]

How much trouble would it be for Red Dragon to include beacons, radio or otherwise?  It occurred to me the one, easiest long-term function the first Dragon could offer for later missions is to provide a landing beacon...naturally under the assumption SpaceX is REALLY thinking long-term (which is often has been).

[IntoTheVoid]

Green: delay of first Red Dragon mission to 2020 opens opportunity to fly a NASA experiment on that mission. #LPSC2017

https://twitter.com/jeff_foust/status/843957105740734464

[Dalhousie]

How much do duststorms obscure sight really? How low would a lander need to go before getting sight of the terrain? This should be known from observations by the rovers. In the worst of the worst dust storms or with sufficiently high probability to ignore the risk?

From orbit, they can obscure the surface completely.  On the surface I think visibility drops to a km km - it's like a thick smog.  I would also worry about contrast effects.  The landmarks might be still visible by the contrast might be so low that the system cannot recognise them.

Of course the proposed landing site is so flat that there are unlikely to be many useful landmarks anyway.

[JamesH65]

How much do duststorms obscure sight really? How low would a lander need to go before getting sight of the terrain? This should be known from observations by the rovers. In the worst of the worst dust storms or with sufficiently high probability to ignore the risk?

From orbit, they can obscure the surface completely.  On the surface I think visibility drops to a km km - it's like a thick smog.  I would also worry about contrast effects.  The landmarks might be still visible by the contrast might be so low that the system cannot recognise them.

Of course the proposed landing site is so flat that there are unlikely to be many useful landmarks anyway.

Don't forget that you could use radar, IR or any non-visible light for which detectors are available to do the imaging. Anything that can get through dust.

[Robotbeat]

I say, just good pre-flight imaging, good geolocation before & after EDL, and a decent gyro. With radar for terminal landing.

[notsorandom]

The SHARAD radar on MRO indicates potential ice deposits in Arcadia a few meters below the surface. They might be too deep for Red Dragon to drill down to but there are ways it could confirm the ice is there without having to do so.

Meteorite impacts have exposed ice at ~1 m depths at this sort of latitude as I understand.

Here is an interesting presentation talking about the radar and the terraced impact craters in the area indicating subsurface ice.

[Dalhousie]

The SHARAD radar on MRO indicates potential ice deposits in Arcadia a few meters below the surface. They might be too deep for Red Dragon to drill down to but there are ways it could confirm the ice is there without having to do so.

Meteorite impacts have exposed ice at ~1 m depths at this sort of latitude as I understand.

Here is an interesting presentation talking about the radar and the terraced impact craters in the area indicating subsurface ice.

Here's a paper showing exposures of shallow ice in small recent craters, some quite close to the proposed site.

[rakaydos]

Out of curiosity, how uniform is the visual appearance of a duststorm?

I'm wondering if a mars "weather sat" could tell a landing red dragon "see that dust bloom?  it's currently 25 km at 25 degrees north from your landing site, and moving 47 degrees west at 5km/hour. I know you cant see your landing site, but believe me, it's down there."

[jpo234]

Peter B. de Selding‏ reports, that Italy's space agency signed a LoI with SpaceX to transport payloads to Mars (see the image).

Peter B. de Selding‏ @pbdes

Despite 2-launch deal w/ @Arianespace, Italy's @ASI_spazio ASI signed a LoI w/ @SpaceX on backup launch of Cosmo-Skymed 2.

[Jcc]

Since the first RD is delayed to 2020, perhaps they will send 2 at that time. This would allow them to try 2 different landing sites, and possibly partner with multiple entities for sensors and experiments. If they both fail, that would be twice as bad, but if at least one succeeds, it would make up for a possible failure of the other. If both succeed, they can make up for time lost after the delay.