Questions & Answers
Answers to the most popular questions about our projects are brought together below. The section is updated.
In order to make manufacturing of the launch vehicle cheaper and simplify it, we refrained from the use of a turbopump in rocket engine design — this is a complicated and expensive part, requiring very long testing to achieve the necessary reliability. So, we use pressure-fed design, which requires high pressure in tanks (high pressure helium enters the tanks and forces the propellants to the engine).
Metal tanks withstand both high pressure and low temperatures, characteristic of liquid oxygen or any other cryogenic fuel, but they are too heavy — this is critical for a small launch vehicle. That is why we use lighter composite tanks, but it is hard to make a composite for cryogenics. Besides, for such a small launch vehicle the cryogenic fuel boil-off (note: oxygen boils at -183 degrees Celsius) can be a serious problem. In particular, Elon Musk faced this problem when creating Falcon-1 launch vehicle.
Peroxide-kerosene combination has a maximum density across all bipropellant combinations. This reduces the size of the tanks, which is particularly important for pressure-fed design. The peroxide has other useful properties. If catalyst package is used, then first the peroxide becomes hypergolic with kerosene, and second we can afterburn the remainder peroxide in monopropellant mode inside the main engine and employ monopropellant vernier thrusters powered by the peroxide (such feature can be useful in the future, though currently we are going to use pressurizing gas for flight control).
We traditionally use geographic names for our launch vehicles. Moreover, the names are allusions to Strugatsky brothers' books: Aldan (river in eastern Siberia) is a computer at NIICHAVO (Scientific Research Institute of Sorcery and Wizardry — Nauchno-Issledovatelskiy Institut CHArodeystva i VOlshebstva) from the novel Monday Begins on Saturday, and Taymyr (peninsula and the northernmost part of the mainland Eurasia) is a spacecraft from the novel Noon: 22nd Century. We, as well as many space industry professionals, grew up on Strugatsky brothers' books.
Aerodynamic losses (for general public — launch vehicle deceleration due to air drag) become quite noticable for a small launch vehicle. Therefore it is important to reduce them, hence to reduce the cross-sectional area of the vehicle.
The second reason is that we manufacture tanks from composite by winding. The larger the diameter of tank, the more expensive filament-winding machine is, but we want to make our launch vehicle cheap.
Lin Industrial team is familiar with the experience of creating amateur liquid-propellant rocket engines by MGLR team and by New MosGIRD team, as well as amateur "hybrids" by Private Rocket Technologies team.
The experience of these teams shows that creating a stable running hybrid engine is perhaps even greater challenge than creating a pressure-fed liquid-propellant engine with comparable thrust.
Reusability is a tough challenge. We are not going to deal with it in early flights.
Currently we are thinking about the flight control for spent rocket stages with gas-powered vernier thrusters and grid fins, so that impact sites could be reduced.
Should the problem of alienation of land for impact sites become important, we will have to catch the stage with a multirotor. This is to be attempted during the test flights of prototype rockets.
Grid fins have the following advantages:
1. Reduced torque and hence reduced power and mass of fin actuators.
2. Reduced shift of aerodynamic center caused by the transition to supersonic speed — there is no need to complicate the flight control algorithms.
3. No fin control reversal characteristic of planar fins at Mach 2.1–3. Control reversal is a phenomenon which causes flight controls to reverse themselves at high speed, so when the fins are deflected in the same direction the rocket suddenly rotates in the opposite direction.
Grid fins generate higher drag compared to planar fins, but provide higher stability for the rocket.
In the current design of Taymyr the helium is fed under high pressure into the propellant tanks and forces the kerosene and peroxide to the engine, where the kerosene and peroxide burn. Theoretically part of the peroxide can be pumped into a separate small gas generator, where it can be decomposed with a catalyst and converted into steam. The steam is a mixture of hot water vapor and oxygen.
Theoretically this steam can be fed back into the propellant tanks to force the kerosene and peroxide to the engine. Then we could eliminate the tank for pressurizing gas. But in reality this design will not work.
If we attempt to force the kerosene by steam, then they will likely explode on contact, because unlike helium, which is inert (i.e. not chemically reactive) and has ambient temperature, the steam is hot and contains oxygen, which burns with kerosene. Besides, only ideal steam would contain just water vapor and oxygen, but in reality it will contain undissociated molecules of peroxide and atomic oxygen. Upon contact with this gas the kerosene would start binding to oxygen atoms, releasing heat, that is, simply speaking, would begin to burn and explode.
Forcing the peroxide by steam also leads to no good. The peroxide is temperature sensitive, therefore when coming into contact with hot steam it would begin to dissociate rapidly into water and oxygen, releasing heat, that is to explode. Even if it will not explode somehow, then water vapor from the steam would dissolve in the peroxide and dilute it, rather than force it from the tank.
Still, the propellants can be forced by the steam, provided first the steam is cooled and second a separator is installed inside each tank (e.g. piston or flexible membrane) between the steam and the propellant. But this is much harder to do than simply to force the propellants by pressurized helium.
Electric batteries are too heavy and accumulate insufficient energy (or more accurately, have insufficient energy density, J/kg). Besides, if batteries are jettisoned, then impact sites become larger — this in turn requires additional approval before each launch. Not to mention that no one has yet developed rockets with electric turbopumps and jettisonable batteries, so such a design would require long testing.
From the other hand, our engine cooling design does not require very high pressure. Therefore, we can do with pressure-fed design, without a turbopump. And, of course, pressure-fed design is simpler.