Please create an account to participate in the Slashdot moderation system

 



Forgot your password?
typodupeerror
Note: You can take 10% off all Slashdot Deals with coupon code "slashdot10off." ×

Comment Re:how low can it go? (Score 1) 43

Clearly it is at a good height now for imaging the whole surface, but as there is no atmosphere could it get down to a mountain scraping orbit? Just high enough to get round the lumps and bumps and variability in the roundness of the object? Would that enable it to image things at a really small pixel size?

Not really. The lower your orbit, the faster your spacecraft has to fly to maintain that orbit.

True, but in zero gee and with no atmosphere that isn't really a problem. It would take some time and reaction mass to get into such a low orbit. The problem is the uneven gravity field -- see my other post,

Comment Re:how low can it go? (Score 4, Informative) 43

as there is no atmosphere could it get down to a mountain scraping orbit? Just high enough to get round the lumps and bumps and variability in the roundness of the object? Would that enable it to image things at a really small pixel size?

Apart from the question of what range the instruments were designed tooperaqte best at, the other problem is the unevenness of Ceres gravity. They are mapping that now, but it's unlikely the mass of Ceres is perfectly symmetrically arranged, so the gravity will be uneven. Those unevennesses distort the orbit and cause it to change over time. If you're 300 km away that's not a big problem, except that you occasionally have to use up some reaction mass to get back where you want to be. At 10km it would probabl;y be disasterous.

For the same reason it's very hard to keep a probe in a stable orbit less than 100km or so above Earth's moon.

Comment Re:Storage (Score 2) 309

Demand is generally higher during the day, so at least for a while this will mean a less variable demand on other supplies, not more.

Moving water up hills (or not letting it down -- letting hydro reservoirs fill up) is quite a good storage option on this scale.

Demand can also be shifted to some extent. You can within certain limits, choose when to cool a refrigerated warehouse, or charge an electric car. I imagine tarifs that make electricity cheap in the few hours after dawn and expensive in the few hours after sunset, for instance.

For the last awkward gaps, methane plant can be built that is designed to switch on and off quickly and run at a relatively low duty cycle. If you're that desperate you can make the methane from CO2 (or food waste).

I've seen reports significant gains in efficiency of making diesel from CO2 and electricity, to the point where that may become a storage option.

Comment Re:Lowcost? (Score 1) 75

That is precisely what the paper linked in the article is about. They identify about 50 GHz of bandwidth (separately for uplink, downlink and interlink) at frequencies between 10 and 250 GHz. At those frequencies beams can easily be kept pretty narrow, so multiple beams will not interfere.

Comment Re:Lowcost? (Score 1) 75

Tracking a few thousand active satellites is trivial, especially as they are radio transmitters and are probably telling their base stations where they are pretty often to allow groundstations to aim their beams.

Since they are in LEO they will not last long once they are out of use. Even if they all failed catastrophically it would be a problem for a few years at most.

Comment Re:Only if it works (Score 1) 337

Small ones are, for basically the same reason that small steam engines were hard to develop initially -- too much surface to leak heat compared to the volume of interior. Big ones are expensive and technical to build, but there is currently no evidence that they won't be energy-positive. This article reports some theoretical engineering progress that might move the trade-offs usefully.

Comment Re:Now what? (Score 1) 242

I think the Dutch government have something similar to the UK Human Rights Act. This makes the rights defined in the European Convention on Human Rights enforceable in the Dutch courts. The parliament could change that law but unless it does the courts can instruct the executive in how to apply the law so as to maintain those rights.

A quick google also suggests that international treaties which the Netherlands has ratified may be directly enforcable in the Dutch courts without needing additional laws to be passed implementing them (as would be the case in the UK). This seems to be a confused area, but it sounds like the court is taking this line.

Comment Re:One problem I see... (Score 2) 242

Mainly embarrass them publicly. Perhaps as the date gets closer if there is no realistic plan and/or no progress they will start issuing more specific instructions. A bit like the US federal courts when states don't do things they are constitutionally required to -- they start out saying "make it so" and get as detailed as they are forced to.

Comment Lots of Much smaller swaps (Score 1) 130

This made headlines because it's the longest cycle ever, but the people who run these programmes see long cycles as undesirable -- what they mostly do is identify hundreds of opportunities for two or three way swaps, or for "open" chains where one altruistic donor can result in two or three people getting kidneys. The maths behind it is quite interesting.

"You need tender loving care once a week - so that I can slap you into shape." - Ellyn Mustard

Working...