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Comment Re:What governmen brought to the table (Score 1) 66

SpaceX and Blue Origin would not use solids, not because there's something wrong with solids per se, but because they're not "fuel and go", which makes them expensive to reuse - and SpaceX and Blue Origin are all about reuse.

A lack of experience with hydrolox surely factors into the picture for SpaceX and Blue Origin; they'd get significantly higher payload fractions by using a hydrolox upper stage. But they're willing to accept lower payloads in order to simplify their manufacture and ground infrastructure, and in particular because the need their propellants to be storable, and storing LH for long periods is a PITA. Storing methalox is quite difficult, but nothing compared to hydrolox.

Comment Re:What governmen brought to the table (Score 1) 66

Solids really aren't that bad when reusability isn't a concern. They're very high thrust, which is exactly what you want out of a booster, and they're structurally very simple. Their low impulse and high structural mass are not particularly important aspects for boosters. Reuse of solids however gains you very little, because there's so much work in refurbishing them.

Comment Re:What governmen brought to the table (Score 2) 66

That's not the reason you don't use it for a first stage. The disadvantages of hydrolox (which are numerous) are offset by its incredible specific impulse. But for a first stage, specific impulse doesn't matter that much, while thrust matters a lot. Thrust is in large part proportional to fuel density, as a turbopump sweeps out a fixed volume per rotation, so the denser the fuel, the more mass (and generally all else being equal, energy) it pumps per rotation.

Another aspect is that first stages are big, meaning that cost is more important than specific impulse. By contrast, when dealing with an upper stage, a small increase in mass has a huge increase in first stage size, and since first stages are so large and expensive, that's a big cost. So you generally want a higher ISP upper stage. With the caveat that "storability" requirements for engines that need to restart can shift the balance; because hydrogen is so deeply cryogenic it's difficult to store for protracted lengths of time. Also, the longer you plan to have a stage in usage without maintenance, the more you tend to favour simple propellants over high performing ones, particularly when you're dealing with small, light engines. So for example if you have an interplanetary probe you'll tend to favour a self-pressurizing hypergolic system so that you only have to rely on a couple valves working, even though self-pressurizing propellant tanks are heavier and hypergolics tend to be lower specific impulse. Engines that are smaller still are often monoprops for an even greater degree of simplicity.

Comment Re:Abolish NASA, and deregulate aerospace. (Score 1) 146

not quite the average toddler's level of understanding.

Project much?

Spoken like one with no clue at all of NASA's decades of hostility to private enterprise in space. Google for "OTRAG" for one example of a potential competitor that they pulled out all the stops to kill off.

-jcr

NASA

NASA Delays First Flight of New SLS Rocket Until 2019 (arstechnica.com) 66

schwit1 writes: Despite spending almost $19 billion and more than thirteen years of development, NASA today admitted that it will have to delay the first test flight of the SLS rocket from late 2018 to sometime in 2019. "We agree with the GAO that maintaining a November 2018 launch readiness date is not in the best interest of the program, and we are in the process of establishing a new target in 2019," wrote William Gerstenmaier, chief of NASA's human spaceflight program. "Caution should be used in referencing the report on the specific technical issues, but the overall conclusions are valid." The competition between the big government SLS/Orion program and private commercial space is downright embarrassing to the government. While SLS continues to be delayed, even after more than a decade of work and billions of wasted dollars, SpaceX is gearing up for the first flight of Falcon Heavy this year. And they will be doing it despite the fact that Congress took money from the commercial private space effort, delaying its progress, in order to throw more money at SLS/Orion.

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