I think they propose to launch lots of such probes hoping that at least one survives. The main technical difficulty would be IMO acceleration. And I'm not sure if it's possible to send information back from several LY distance, using very limited payload (if any) they'll be able to throw there.
The thread for space cadets!
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The launch cost per device is likely to be quite low, once you have paid for the initial overhead. As described in the picture, they would send hundreds of these and hope that at least a few survive.
Unfortunately, I think 0.2c is overly optimistic, so we are unlikely to see any data in our lifetimes. Nevertheless, it is the most realistic proposal for interstellar probes that I have heard of (which is admittedly a very low hurdle to clear).
warpus
Sommerswerd asked me to change this
They must have done calculations that tell them the statistical probability of one of those probes surviving. Error margin on those calcuations must be large, but I suppose that answers my question
They'll need the SLS for either Moon or Mars. I don't think that Trump will try cut the NASA budget. Space Exploration and Making America great again are basically two sides of the same coin.
hobbsyoyo
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They actually don't need either, especially not as-is. The currently funded and nearly-developed Block I variant can only lift 1.5 - 2.5* times as much mass as the current (and near future) boosters at a much higher cost (2.5 -10** times more expensive). Sure, it can lift heavier payloads than anything else but it won't really enable new types of missions. It is also only funded to fly two more times and only one of those is really 'guaranteed'. Next year's inaugural launch is all but a done deal and the Europa mission has strong backing. But beyond that, we don't know what Trump is planning and it's worth noting he could do a lot more with cheaper commercial options.
The future Block II variant (and the II+ variant with new boosters) would represent a major step change and would enable some great missions of new types if built in quantity. Right now we don't even know if it will be built.
I'm actually reading through an article that claims a White House source has leaked a bunch of information that more or less says 'New Space' won an internal White House debate about a path forward.
We're talking manned cislunar trips by 2020 (actually feasible, I kid you not), private space facilities and factories, and massive increases of commercial utilization of LEO. The article also mentions that NASA will be refocused to work on very large interplanetary missions. I have no idea how idea how reputable Politico is on this topic.
*Payload Comparison
SLS Block I 70 metric tons
SLS Block II 130 metric tons
Falcon Heavy 50 metric tons
Delta IV Heavy 35 metric tons
Long March 5 25+ metric tons (like closer to 40 metric tons when development is finished; flown once)
**Price Comparison
SLS Block I $1b+
SLS Block II $1b+
Falcon Heavy $100m
Delta IV Heavy $300m+
Long March 5 ???
All numbers approximate and all points ceded to someone who wants to drag out citations.
Quite a bit. Falcon 1 could do 670 kg to LEO on a good day and it only actually flew 140 kg before retirement. The PSLV can do 3,800 kg - which is close to what the earliest Soyuz rockets could do. They aren't super comparable and it's also worth noting that a major chunk (88 out of the total) were identical satellites built by the same company (Planet Labs - they sell imagery). This makes it pretty close to the first order estimation you were trying to do and yet-
"The weight of the payload will be 1350 kgs, of which 500-600 kgs will be the satellite's weight," Somnath added."
Which goes to show that simply adding the mass and the volume of a standard cubesat together doesn't give you a great estimation of how many a rocket can launch. ISRO also had a lot of scheduling difficulties between all of the ride-shares which delayed the launch at least once that we know about, likely several times.
Just to re-iterate, space planes just aren't super practical from many points of view. The wings are dead weight for anything but risky plane-change maneuvers, the ability to get some serious cross-range distance during re-entry and highly accurate landing capability. In other words, it can be done and the Air Force currently flies the X-37B space plane while Sierra Nevada Corp is developing the Dream Chaser for unmanned flights to the ISS. The X-37B needs the plane changing capability as a spy sat while SNC is marketing the ability of the Dream Chaser to get a payload from orbit to a scientist's lab in a matter of hours due to landing at air strips. They found a niche use for wings, basically.
For any mission that doesn't require plane changing and airstrip landings, you'd want to use a capsule or not bring the payload back at all.
Oh and India has a development space plane they've flown a few times. They use it to test their airframe and thermal protection system designs at hypersonic velocity before ditching it in the ocean. It's meant to be a pathfinder for a later shuttle program but I don't have a great feel for how committed ISRO is to that program over the long run. I suspect this is purely a research vehicle.
Oh oh and ESA flew a mini shuttle prototype for the same reasons as ISRO a few years ago. More here and here.
Combustion is half the problem, the massive thermal load of flying through the atmosphere (even super high altitude) is the other massive portion of the problem to overcome.
Yes, definitely so. The flight profile will dictate what kind of thermal protection system you use but most definitely a plane that can exit the atmosphere has to deal with tremendous thermal loads.
Thank you.Nice writeup.
Yup, acceleration and communication are basically all these things can do and I'm doubtful we could pull it off without massive direct R&D investment. Even then you'd need a massive infrastructural investment to actually make the scheme work - above and beyond the R&D dollars.
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warpus
Sommerswerd asked me to change this
Well get on it! Let's send that Yeti to Proxima Centauri
warpus
Sommerswerd asked me to change this
What's the ETA on that? If you are allowed to say
hobbsyoyo
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I'm not. Sorry.
This article on SpaceNews gives a lot of credence to the Politico article I linked to earlier. It's also nice to read that work on an upgraded upper stage (necessary for Blocks Ib and II) was actually authorized and is going well. I did not know that.
And apparently the EUS (exploration upper stage, the new second stage) will boost the payload of the SLS Block 1b to 105 metric tons which is awesome and makes the rocket more viable.
This line from Politico was notable:
This article on SpaceNews gives a lot of credence to the Politico article I linked to earlier. It's also nice to read that work on an upgraded upper stage (necessary for Blocks Ib and II) was actually authorized and is going well. I did not know that.
And apparently the EUS (exploration upper stage, the new second stage) will boost the payload of the SLS Block 1b to 105 metric tons which is awesome and makes the rocket more viable.
This line from Politico was notable:
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I am wondering: How viable is it to assemble an interplanetary ship in orbit from a few parts launched separately? Let's say, 4 parts, each on a Falcon Heavy, compared to the complete ship on one SLS Block II. Obvioously, 4 launches is goiing to be less efficient, because you need to get into orbit and then spend fuel for docking maneuvers, but at the same time I would think that building one giant rocket is much harder than building multiple smaller ones.
What mission types would really require an SLS?
hobbsyoyo
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I don't have the imagination required to conjure up all the types of new missions that will be enabled by the biggest SLS rocket but I can give you a summary of what capabilities it will offer. You can draw conclusions on mission-type viability from them.
The key capabilities are:
Larger fairing size, gentler acceleration profiles and excess lifting capacity.
1) Fairing size: This is a limiting factor on a lot of missions. You can only fly something as big as the fairing it's contained in no matter how light it is. Engineers have gotten very good at folding things up (see the James Webb Space telescope unfold below) but there is a limit to this. Even the first batch of free-flying inflatable space habitats will require a brand new fairing (and second stage) for the existing Atlas V rocket to get it to space. Atlas already flies one of the biggest fairings on the market, for reference. Plus, in many cases, folding a satellite up imposes an additional weight penalty for all the hinges, servos, etc as well as a hit to overall reliability for the same reason.
Docking spacecraft together to create a bigger spaceship imposes other, less obvious penalties as well. So, for example, most fuels and oxidizers are liquid at different temperatures which means you have to insulate them from each other with a bulkhead(s). With big tanks, the square/cubed area to volume ratio works in your favor and you can make the bulkheads take up a much smaller total percentage of the entire vehicle than you could with a scaled down vehicle. In other words, you waste more space and mass launching smaller ships than bigger ones.
2) Smaller rockets accelerate much faster than larger ones for obvious reasons. Liquid engines have limited (if any) throttling capabilities, typically less than 30% of the total. Solid rockets can also be built in such a way that they automatically begin accelerating less (or more) as they burn down due to changing internal fuel geometry. This is even less limited in throttling ability than similar sized liquid engines.
What I'm getting at is that for smaller rockets, there tends to be less ability for the rocket to limit its own acceleration. Payloads have to deal with this which means more dead weight is spent beefing up the load path within the satellite and in its payload adapter. Very large rockets, by their vary nature, tend to accelerate much more gently than their smaller cousins. This means more delicate sensors and satellites can be flown or larger satellites of traditional construction can be launched.
3) Certain missions have absolute limits on the minimum mass they require. Let's say that landing on Europa will take 10,000 kgs of fuel and oxidizer just to land the empty tanks. What this means is that no matter how light you can make your sensors, you still have to get 10,000 kgs to Europa to be able to do anything. If you don't have a launcher that can do that, you will never be able to land on Europa.
Alternatively, you can launch a smaller craft towards its destination at a much faster velocity. I've been doing some reading and this is a highly desirable and often-sought ability for manned interplanetary voyages. Most mission plan proposals for human interplanetary trips assume very long transits but this is only because they are designed around the very limited (compared to the task, not in absolute terms) rockets that are currently available. Given a larger rocket, mission planners would opt to get to the destination and back as quickly as possible and make mass savings in the payload to do it. As shown in the paragpraph above, however, there is a certain physics-dictated limit to how much mass you can save on certain mission types. The SLS effectively raises that lower limit with its excess lifting capacity in a way few rockets can do.
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Thank you for the explanations. But I am not sure I fully understand this point:
Does this assume a minimum area density of the tank hull and a maximum exhaust velocity? I get that if you have a given specific impulse the mass of the fuel will limit the total mass of the spacecraft you can land. If the tank that is necessary to contain that fuel weighs more, you are never going to land that ship, no matter how light the rest is. This means that for any given material and necessary hull thickness (which results in a minimum area density) you can calculate a minimum weight of the tank that will be able to land. And if you cannot land a single tank, bringing more of them is not going to help. But you could - at least in theory - improve on that by either improving the efficiency of the engine or select a hull material with less area density. With current technology, there is going to be limits to these options, so you end up with a hard limit. But I would not call this a physical limit, unless you can show that you cannot improve on these technology limits for some reason.
Does this assume a minimum area density of the tank hull and a maximum exhaust velocity? I get that if you have a given specific impulse the mass of the fuel will limit the total mass of the spacecraft you can land. If the tank that is necessary to contain that fuel weighs more, you are never going to land that ship, no matter how light the rest is. This means that for any given material and necessary hull thickness (which results in a minimum area density) you can calculate a minimum weight of the tank that will be able to land. And if you cannot land a single tank, bringing more of them is not going to help. But you could - at least in theory - improve on that by either improving the efficiency of the engine or select a hull material with less area density. With current technology, there is going to be limits to these options, so you end up with a hard limit. But I would not call this a physical limit, unless you can show that you cannot improve on these technology limits for some reason.
hobbsyoyo
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You're welcome.
Yes. You summed it up very nicely yourself.
You're not wrong it's just that there are technology limits we cannot over come.
With chemical combustion, which is the only source we have that is able to produce a greater than 1.0 thrust-to-weight ratio in all gravity fields, you're not going to go over about 470s specific impulse. Theoretically you could use a fluorine compound as an oxidizer which might bump that but the draw backs are enormous - so much so that it just wouldn't be done. I can expand on this point if anyone would like to read it but suffice it to say, there is a hard limit to the efficiency of chemical combustion that can't be overcome.
Even then, you can't actually operate at that bleeding edge of efficiency. Hydrogen is proton-sized so given a long transit, it will slip through the tank walls through proton-sized cracks - you can't get rid of those. While it does this, you're not only losing your fuel but your tanks begin to get brittle which is its own problem. Additionally, Hydrogen is such a deep cryogen that you would have an extremely hard time keeping it all from boiling off during transit without a very large, massive and power-hungry refrigeration system. In other words, spacecraft won't even be able to use hydrogen (max efficiency) engines unless they are big enough to have the kinds of systems that would keep hydrogen from boiling off. For that you need a massive rocket.
The only non-chemical reaction source that could plausibly be used for landing missions is nuclear thermal rockets. For these, again you'd need a massive rocket to haul up a nuclear reactor because reactors and their shielding can only shrink so much and still be useful. I actually worked on a preliminary design for a pulsed nuclear-thermal rocket engine for small satellites in college with the nuclear science research team. There was most definitely limits on how small you can shrink that kind of technology and still have it work. A lot of that is driven by atomic cross sections and other physical, intrinsic properties that can't be altered outside of the Large Hadron Collider, if you get my meaning.
On increasing hull mass efficiency - we're pretty much at that point right now with most modern second stage* designs. You can always eat away at some margins but there is not a step-change to be had unless materials science makes its own step change advancement.
*Second stages are much more mass sensitive than first stages thanks to the rocket equation. Roughly speaking, you can add about 9-10 lbs of mass to a first stage and only lose a 1 lb of payload. For second stages, it is 1:1 so they are designed with every mass-savings trick that engineers can muster.
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hobbsyoyo
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Apparently the Trump administration is going to close the Export-Import Bank. How's that for supporting American manufacturing? 
This bank was very important to allow foreign firms to finance rocket and satellite purchases from American companies. The space business is inherently risky and expensive and this bank helped industry enormously. Other countries (and super-national entities like the various European companies/agencies) have their own version of the Ex-Im bank and use it to help their own industries.
Somehow Republicans have come to see the Ex-Im bank as corporate welfare, unlike coal and gas subsidies. Yes, the bank provides below-market financing but with so many other nationally-backed banks doing the same thing you could almost argue that below-market financing is the market.
Link
The Juno probe is staying in its initial check-out orbit. It arrived at Jupiter in a very elliptical orbit which was then supposed to be lowered into its final 'science' orbit. A stuck valve prevented that maneuver from happening and though NASA has tried to find a way forward, they finally decided just to leave Juno where it is. It will take much longer to return the originally-planned amount of data from this orbit which carries its own risks.
Link
The Proton rocket has been grounded for a few months as they sort out engine problems. The engine manufacturer swapped materials they used in their construction which resulted in failures during launch and testing. The narrative is a bit muddy as the Russians have claimed alternatively, 'Nothing is wrong' and 'We fired the guy who made problems that are fixed now' but its clear that their is actually a problem that will take a while to sort out. The same engines are used in at least some variants of Soyuz but the impact to that system (beyond the failures that already happened) are unknown at this time.
Link
This bank was very important to allow foreign firms to finance rocket and satellite purchases from American companies. The space business is inherently risky and expensive and this bank helped industry enormously. Other countries (and super-national entities like the various European companies/agencies) have their own version of the Ex-Im bank and use it to help their own industries. Somehow Republicans have come to see the Ex-Im bank as corporate welfare, unlike coal and gas subsidies. Yes, the bank provides below-market financing but with so many other nationally-backed banks doing the same thing you could almost argue that below-market financing is the market.
Link
The Juno probe is staying in its initial check-out orbit. It arrived at Jupiter in a very elliptical orbit which was then supposed to be lowered into its final 'science' orbit. A stuck valve prevented that maneuver from happening and though NASA has tried to find a way forward, they finally decided just to leave Juno where it is. It will take much longer to return the originally-planned amount of data from this orbit which carries its own risks.
Link
The Proton rocket has been grounded for a few months as they sort out engine problems. The engine manufacturer swapped materials they used in their construction which resulted in failures during launch and testing. The narrative is a bit muddy as the Russians have claimed alternatively, 'Nothing is wrong' and 'We fired the guy who made problems that are fixed now' but its clear that their is actually a problem that will take a while to sort out. The same engines are used in at least some variants of Soyuz but the impact to that system (beyond the failures that already happened) are unknown at this time.
Link
Synobun
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The NASA team is doing an AMA on reddit right now about the discovery they've released today regarding the star system with 7 Earth-size planets.
Zkribbler
Deity
They're in close orbit around an untracool dwarf. All may have surface water. Here[s the CNN article:
http://edition.cnn.com/2017/02/22/world/new-exoplanets-discovery-nasa/index.html
warpus
Sommerswerd asked me to change this
Summary of the announcement, done by somebody on reddit:
1) Spitzer detects 7 earth size planets around the TRAPPIST-1 Star System
2) 40 light years away
3) 3 planets are in the right zone for liquid water
4) Have measured the masses and radi of earth-size planets
5) Can look at atmosphere and bio-signatures
6) Planets are close to each other, you would see them similarly as you would see Earth’s moon.
7) Planets are so close, they interact gravitationally on each other.
8) Trappist-1e is very close in size to earth. It receives a similar amount of light as Earth does.
9) Trappist-1f (MIGHT) be water-rich and similar in size as earth (NASA just said currently no detection of water). Receives about as much light as Mars.
10)Trappist-1g is largest in the system, 13% larger radius than Earth. Receives about as much light as Mars and the Asteroid belt.
1) Spitzer detects 7 earth size planets around the TRAPPIST-1 Star System
2) 40 light years away
3) 3 planets are in the right zone for liquid water
4) Have measured the masses and radi of earth-size planets
5) Can look at atmosphere and bio-signatures
6) Planets are close to each other, you would see them similarly as you would see Earth’s moon.
7) Planets are so close, they interact gravitationally on each other.
8) Trappist-1e is very close in size to earth. It receives a similar amount of light as Earth does.
9) Trappist-1f (MIGHT) be water-rich and similar in size as earth (NASA just said currently no detection of water). Receives about as much light as Mars.
10)Trappist-1g is largest in the system, 13% larger radius than Earth. Receives about as much light as Mars and the Asteroid belt.
stfoskey12
Emperor of Foskania
Could humans be leaving low Earth orbit for the first time in 46 years?
http://www.space.com/35844-elon-musk-spacex-announcement-today.html
http://www.space.com/35844-elon-musk-spacex-announcement-today.html
