The case for a pressurised lunar rover.

[Eric Hedman]

As stated previously, Toyota is the company with the most debt worldwide.

Toyota's previous CEO. The company founder's grandson was push aside recently after years of Toyota slow walking developing an BEV of their own, cheating on car emissions and lobbying governments worldwide against banning ICE vehicles. Also the previous CEO is the chairman of the Japanese automobile Manufacturering Association, stills wield influence over all Japanese car manufacturer against EV adaption.

Having the most debt is not a problem if they have the cash flow to service the debt and if the debt is at a low enough interest rate.

Akio Toyoda, the CEO is not being pushed aside.  He is becoming Chairman of the Board.  At age 66 he no longer wants to do the strenuous work of day to day operations.  This move was triggered by the retirement of the previous board chairman.  As Board Chairman he will have more of an ultimate say on the direction of the company than he did as CEO.

[MickQ]

I just read that Honda is to provide hydrogen fuel cell expertise to the lunar cruiser project.  The Nikkei article said that they expect a range of 1000 klm from a full load of hydrogen and oxygen.
The fuel cells are onboard the rover while the Virginia Polytechnic design uses a trailer mounted RTG to provide power and heat.

The fuel cell version depends on water electrolysis and the problems of hydrogen storage/handling while the radioisotope method has the radiation problem thus the towed trailer mounted power supply.

I prefer the rtg as it provides 24/7 power and heat without refueling but would require a large amount of heat source, of whichever type you prefer.  Maybe a trailer mounted Kilopower would work.

Which would be the better option ?

[Robotbeat]

You know… if you compare the weight of compressed hydrogen and oxygen tanks plus the fuel cell, radiator, and associated plumbing, and the inefficiency of a fuel cell… you aren’t any better than state of the art lithium based batteries which get >450Wh/kg. Especially if you’re doing a regenerative system which captures the water. 1000km battery range is feasible and then you can easily recharge just with some lightweight solar arrays (or pre-placed solar/battery powered recharging stations).

RTG wouldn’t be bad, but is kind of expensive for the powers you’d like.

[chopsticks]

1000km battery range is feasible and then you can easily recharge just with some lightweight solar arrays (or pre-placed solar/battery powered recharging stations).

Wouldn't recharging a big battery pack like that take a really long time with solar, unless you had a huge array? Amy approximations as to what size of an array would be required to recharge in say 1 day? I remember seeing a video from Engineering Explained where he goes over what it would take to keep a road car moving under full sunlight, it's not easy. (I'm not suggesting that for a rover, but it went on to show just how much solar is actually required for it to be effective)

Preplaced stations sounds neat, but a bit far out until some amount of infrastructure is built up.

[joek]

Wouldn't recharging a big battery pack like that take a really long time with solar, unless you had a huge array?
...

Likely would take quite a while if the MO was: driive until batteries near depleted, recharge; repeat. However, that is not likely to be the MO for the foreseeable future. More like: dirve for 8-12hr; crew rest-recharge for 12-16hr; repeat. Not to mention that for safety reasons, excursion distance will be limited.

So a few basic assumptions. All numbers approximate. Also sandbagging a bit here and reducing these numbers by ~10% from current state-of-the-art...
- Lunar surface solar insolation: 1300w/m²
- Solar panel efficiency: 30%
- Charge system efficiency: 95%
= Effective charge rate: 370w/m²
- Rover solar panel size 2x3m (e.g., ROSA) = 6m²
= Effective total charge rate: 2.2kW/hr

So what does a charge rate of 2.2kWH get you in terms of range? A Tesla S on Earth gets ~5km/kWH. Assuming similar for our lunar rover, every hour charging would get our rover ~11km. (Which I doubt is a reasonable comparison... Tesla S on Earth and hypothetical lunar rover are likely to be very different, with the Tesla S on Earth being more inefficient.)

If we assume (1) During every 24hr cycle we have 12hr of rest-rechange and 12hr drive time, each cycle would get us ~130km, or ~7.5 days to reach 1000km excursion @11km/hr.  If we assume (2) every cycle is 16hr rest-recharge and 8hr drive time, each cycle would get us 176km, or ~5.5 days to reach 1000km excusion @22km/hr.

NB: Those power-range-time estimates are based only on power available-consumed, not other limitations such as speed; e.g., for (2) 22km/hr is likely excessive for unexplored areas.

In short, believe power-range should not be an issue with current state of the art.

Which brings us back to the topic at hand... Yes, need a pressurized rover for excursions beyond more than a few hours or km. Power should not be a problem.

edit: thanks @TheRadicalModerate -- think got the brain farts corrected.

[TheRadicalModerate]

= Effective charge rate: 370w/m²
- Rover solar panel size 2x3m (e.g., ROSA) = 6m²
= Effective total charge rate: 2.2kW/hr

So what does a charge rate of 2.2kWH get you in terms of range?

Nit:  You've got some unit mangling going on here.  Charge rate is 2.2kW, not 2.2kW/hr.  Nor is 2.2kWh a rate--it's energy.

[TheRadicalModerate]

I can't find the video, but somebody posted an interview with one of the Dynetics program managers, who talked in passing about ALPACA's ability to accommodate a lunar rover docking directly with the low-slung crew module.  That would allow shirtsleeve transfer of the crew from a lander to a hab.  Nice feature--and certainly a case for pressurized rover.

But not necessarily a pressurized rover with hundreds of km of range.

[TrevorMonty]

I can't find the video, but somebody posted an interview with one of the Dynetics program managers, who talked in passing about ALPACA's ability to accommodate a lunar rover docking directly with the low-slung crew module.  That would allow shirtsleeve transfer of the crew from a lander to a hab.  Nice feature--and certainly a case for pressurized rover.

But not necessarily a pressurized rover with hundreds of km of range.

Was ALPACA carrying rover and crew or just ability to transfer crew to rover already on surface.

The ALPACA design can be used for carrying large cargo like pressurized rover. Just replace  crew habitat with low slung platform and ramp.

[TheRadicalModerate]

Was ALPACA carrying rover and crew or just ability to transfer crew to rover already on surface.

The latter--the rover would come out to pick up the crew and take them to the hab (or vice versa).

I'm not sure that ALPACA would have enough clearance to drop a human-habitable rover in one mission.  Maybe a "rollerskate" in one mission and a hab to fit on top of it in another?  But that would require a way for the rollerskate to winch the hab into position.

[whitelancer64]

The mass of a sarcophagus to shield modern electronics from radiation is heavier than if you just use vacuum tubes. 

There is no way a vehicle can roll down a ramp from Starship’s cargo bay to the lunar surface.  Everything being.dreamed of has to have its own descent and landing capability.

Who said anything about a ramp?

[TrevorMonty]

Was ALPACA carrying rover and crew or just ability to transfer crew to rover already on surface.

The latter--the rover would come out to pick up the crew and take them to the hab (or vice versa).

I'm not sure that ALPACA would have enough clearance to drop a human-habitable rover in one mission.  Maybe a "rollerskate" in one mission and a hab to fit on top of it in another?  But that would require a way for the rollerskate to winch the hab into position.

Landing with rover should be straightforward but launch would require rover to be strapped side ways on lander and experience launch G forces sideways.