Consider the "Tyranny of Rockets" problem: if you want to send a rocket up 1 km, you need X fuel. But to get to 2 km, you need way more than 2X fuel- because you first have to carry all that extra fuel up 1 km, which takes more energy/fuel, before you can use it to go the other km. And if you want 3 km up... well, you get the idea. It's exponential in cost.
Then the problem of the fuel itself. It has to be something super-energy-dense: lots of energy (velocity) for the least mass. The most super energy dense substances are usually used to make bombs, so basically you're building a metal tube with explosives inside and hoping that you can direct the explosion correctly such that your rocket goes up.
And then you have to make sure your payload- in this case some sensors to prove you actually went up that high- have to be lifted (mass) and not break. In the case of this team, their previous rocket probably did reach space but the sensors weren't working so they have no evidence!
If you want to really learn this stuff, play the game "Kerbal Space Program". It's not accurate in any sense, but it gives you the instincts of why and how rocketry and orbital mechanics work.
>The most super energy dense substances are usually used to make bombs,
By volume or per mass high explosives usually don't have much energy density compared to things like liquid fuels (ie, gasoline) or even solid fuels. This holds true for all high explosives (substances used to make bombs). They're all pretty low energy density. They're just high power because of the low time to release the energy.
Delta-v, as used in spacecraft flight dynamics is a measure of the impulse that is needed to perform a maneuver such as launch from, or landing on a planet or moon, or in-space orbital maneuver. It is a scalar that has the units of speed. >>As used in this context, it is not the same as the physical change in velocity of the vehicle<<.[1]
To clarify: is the distinction between delta-v and change in re velocity that thrust could be applied in any direction, including in the braking direction, so a rocket applying a maneuver of given delta-v could end up with an increased or decreased (or zero) final speed?
If the above distinction is correct, then in general delta-v is not coupled to the physical change in the rocket's velocity. But in the case of a conventional rocket with a fixed thrust vector launching from Earth's surface (as in OP's comment), isn't it perfectly true that delta-v is equivalent to change in velocity (barring air resistance)?
>Consider the "Tyranny of Rockets" problem: if you want to send a rocket up 1 km, you need X fuel. But to get to 2 km, you need way more than 2X fuel- because you first have to carry all that extra fuel up 1 km, which takes more energy/fuel, before you can use it to go the other km. And if you want 3 km up... well, you get the idea. It's exponential in cost.
Is this correct? I know how the Tyranny of the Rocket Equation relates to mass, but I've never heard it used in terms of altitude before. Using the kinematic equations, it seems the initial velocity required to reach height 2X would actually be less than double of that for just X. However, I'm not sure if that also applies to rocket launches and if it does how it relates to fuel requirements.
Feel free to correct me if I'm on the completely wrong track here.
It's not correct. The rocket equation is exponential for delta-v, not for altitude. Getting to 2km could easily be free once you've hit 1km, if your rocket is traveling fast enough at 1km when it cuts out to coast much higher.
It's getting to, say, 2 km/s that takes more than double the fuel of getting to 1 km/s. It's not a simple relationship though (like say the inverse-square law); it's related to propellant velocity, which for chemical rockets is in the neighborhood of 4 km/s. Reaching velocities greater than your propellant velocity is where the exponential ramp really starts to take off.
And no, it's not just mass either. If you have a rocket that sends mass M to velocity V, then double the size of the rocket and it'll send mass 2M to velocity V. The rocket equation tells you the ratio of fuel mass to payload mass required to reach any given delta-v. That's what grows exponentially as the desired delta-v grows.
Assuming ample money, resources, and support, height isn't a big deal (for solid state rockets).
From my experience as a part of a collegiate (liquid) rocket club, just getting to manufacturing is a major hurdle.
There's legal red tape, university specific red tape, insurance/liability, material sourcing, funding, manufacturing, testing etc.
Note that some of these steps may require specialized facilities/equipment, transport, etc. Outsourcing (e.g. manufacturing) trades off for added red tape. ITAR is fun.
This makes working towards great heights a slow process, and if something goes wrong during testing/launch it's a major set back.
> For most of the history of spaceflight, sending a rocket to space required mobilizing resources on a national scale.
From the article. It's not that it is super hard to do nowadays if you have a near endless supply of resources and money, but for students in a science project it is a big deal.
If you accept premise of unlimited budget and outsourcing, sending something to space is about as difficult as saying “Hey Elon, I want this thing to go to space.”
The point here is that college students are able to pull this off with a small budget and lots of DIY.
i've been in the high power rocketry hobby for a year or so.
Mostly it's getting everything to go right a the same time. Fin flutter destroys rockets, so does wind sheer, so does bad flight controllers or bad programming. Parachutes not deploying properly in low pressure high altitude flights, second stage igniters not working as fast as they should at low pressure, the list goes on and on.
The below forum is pretty much ground zero for the hobby in the United States IMO. There's some very very talented regulars there who are truly pushing the limits. All the owners of the electronics and software used in the hobby are on this forum too and post regularly. Many University teams show up on this forum too, i believe this USC team is there from time to time asking for advice.
By and large, as long as you're using decent specific impulse propellants, the hard part is not really the rocket equation but rather that rockets are extremely complicated sustained explosions. Oh, and they're really expensive. You have to worry about pogo, combustion instability, etc.
What else besides power/weight ratio is required to achieve something like this?