Solar Thermal for Ground Launch

eliaslor · 2014-02-04 17:18:57

Hi, I read a Wikipedia article that suggests that there is technology being produced that will allow small rocket ships to be launched from land using solar power and an ammonia propellant. Does anyone here have an opinion on the likelihood of this technology being produced and used in the near future (the next 100 years)? Any help would be appreciated. Here is the excerpt from Wikipedia:

Solar thermal rockets have been proposed [7][full citation needed] as a system for launching a small personal spacecraft into orbit. The design is based on a high altitude airship which uses its envelope to focus sunlight onto a tube. The propellant, which would likely be ammonia, is then fed through to produce thrust. Possible design flaws include whether the engine could produce enough thrust to overcome drag, and whether the skin of the airship wouldn't fail at hypersonic velocities. This has many similarities to the orbital airship proposed by JP Aerospace.

Source: http://en.wikipedia.org/wiki/Solar_thermal_rocket

Terraformer · 2014-02-05 03:43:47

Awkward... recursive loop... that idea was proposed here ages ago by a member who hasn't been around since before I joined, and that's where the idea comes from. Here is Tom Jolly's proposal, and here is the original thread.

GW Johnson · 2014-02-05 12:18:25

Frontal drag will always be an insoluble problem for supersonic/hypersonic blimp ideas, no matter what kind of rocket you try to push it with.

GW

RGClark · 2014-03-09 15:44:32

GW Johnson wrote:

Frontal drag will always be an insoluble problem for supersonic/hypersonic blimp ideas, no matter what kind of rocket you try to push it with.
GW

Drag will be a problem for solar thermal launch from the ground. But I don't rule it entirely. For instance it doesn't have to be a blimp. It could be like, say, a large supersonic aircraft such as the XB-70 where the focusing lenses or mirrors cover the entire wing.

Bob Clark

JoshNH4H · 2014-03-09 17:42:43

Hi Eliaslor! Welcome to NewMars!

It's certainly a very attractive idea, and solar thermal propulsion is not without it's uses. However, there are two significant issues with Solar Thermal for ground launch, as I see it.

The first of these is power usage. Let's say we're using a lifting body design (Highly non-trivial!) on a 9.5 km/s trajectory to LEO. Let's say your craft has a Lift to Drag ratio of 4 (not optimized for any particular speed, this is a very good one). Let's say you want 10 tonnes of payload and your structural mass fraction is equal to 15% of the fuel mass. Let's say you get an Isp of 875 s.

The mass ratio will be 3.0. Gross Liftoff Weight will be 45 tonnes, and fuel mass will be 30 tonnes. If the Thrust-to-weight ratio of the rocket is .3 [This is very much a lowball value, even given the optimistic lift to drag ratio I assigned to this craft], it will be necessary to produce 126 kN of thrust. At 875 s, this necessitates the use of 14.7 kg/s of fuel. Assuming an engine efficiency of 70% (High), this will necessitate an engine power of 154 GW.

Assuming an insolation of 1000 W/m^2 (very high for Earth's surface) this will necessitate 154 square kilometers of concentrating mirrors. This is about three times larger than the area of Manhattan, and almost as large as all of the city of Toronto.

And this is only for 10 tonnes of payload. Still think it's a good idea?

Pointing is another issue. Parabolic concentrators need the sun to be directly over head at all times in order to function properly. This is pretty hard to do when you're moving at a speed of multiple kilometers per second.

So, this one's a no. But stick around and I'm sure you'll be coming up with good ideas left and right

SpaceNut · 2014-03-09 20:45:18

Ammonia propellant exhaust dissociates into hydrogen and nitrogen sounds like elctrolysis... but the combustion of ammonia in air is very difficult in the absence of a catalyst (such as platinum gauze), as the temperature of the flame is usually lower than the ignition temperature of the ammonia-air mixture. The flammable range of ammonia in air is 16–25%. The combustion of ammonia to nitrogen and water is exothermic: 4 NH3 + 3 O2 → 2 N2 + 6 H2O (g) (ΔH°r = −1267.20 kJ/mol)
http://www.astronautix.com/props/loxmonia.htm

GW Johnson · 2014-03-10 16:20:50

Solar, whether thermal or PV, tends to be a "low density" and rather "slow" energy source, here on Earth. It's worse yet further out from the sun. Dunno, might be better at Mercury. 10 times higher light flux there.

What about using solar as a way to derive and store the captured energy in a different form? A form that can be used very rapidly. One example is solar electrolysis of water into LOX and LH2. Liquify them, requiring more energy yet, which in principle could also be solar-derived. Then burn those propellants "suddenly" in a rocket engine, to go where you want to go. That way your vehicle need not carry around all the gear required to make its energy source.

GW

tahanson43206 · 2025-01-26 11:28:49

GW Johnson's recommendation for Post #7 of this topic seems to hold up pretty well ten years later.

We have plenty of incoming solar power, thanks to the output of the Sun, most of which we humans are not using.

GW suggested using that solar energy to create rocket fuel that works with existing chemical rocket designs.

If someone were to actually carry out that recommendation, it would show that the goal of the topic is reachable.

We are using ** stored ** solar power right now to reach orbit, and eventually that handy store we've been draining is going to run out.

(th)

Calliban · 2025-01-27 09:59:09

Solar thermal heat could be used to provide launch assist by heating up water and powering a steam rocket. We have also discussed the use of steam cannons in the past as a way of providing launch assist. In both cases, we are looking to boost a rocket to circa Mach 1 at takeoff. The idea is to provide enough of a boost to eliminate need for a first stage, allowing the boosted rocket to work as an SSTO. This cuts out a sizable chunk of the capital and operating cost of a space launch system.

But there are problems. The launch assist comes with its own capital and operating costs. In fact a launch assist is a piece of infrastructure that will cost substantially more than fabricating a single first stage. Its economics depend upon rapid reusability. It could allow sizable savings over a large number of flights. Keeping marginal cost to less than that of a first stage implies a minimal launch rate. Also, a single launch accident could damage or destroy the launch assist. Also, the economics are less favourable if the first stage can be made rapidly reusable anyway. Which seems to be the direction that SpaceX are taking.

kbd512 · 2025-01-28 13:05:52

US Navy History with Steam, Electric, and Internal Combustion Aircraft Catapult Launch Systems
The US Navy tested and rejected the forerunners of EMALS (Westinghouse's electro-pult) and C-14 combustion catapults (ICCALS) back in the 1950s as being too immature and unreliable when compared to steam. All three technologies were basically functional, but lacked the refinement and reliability of steam. One of the three candidate aircraft catapult launch technologies was to be installed on America's first nuclear powered aircraft carrier, USS Enterprise, CVN-65.

Steam is decidedly more maintenance intensive than EMALS and ICCALS, but when it breaks down an immediate fix is typically practical to implement without taking down the entire system. EMALS requires waiting 90 minutes for its flywheels to spin-down, and a fault with one electrical power transfer subsystem takes down all 4 connected aircraft catapults at the same time. That is unacceptable for a warship conducting combat flight operations, but also not acceptable for a commercial launch operation venture with a launch schedule to maintain, because time is money. In combat, time is life or death. Steam reliability remains superior when compared to electricity and combustion.

Steam's primary advantage over EMALS or ICCALS for a land-based launch system is the enormous quantity of steam that a large solar thermal or nuclear thermal power plant can generate and temporarily store for a launch. Water and heat from the Sun are available in staggering quantities, at low cost. After the plant equipment is fabricated and installed, so long as sliding parts are lubricated and wear parts periodically replaced, steam power reliability is pretty much a given. Storing small quantities of electrical power has proven exceptionally difficult, expensive, and EMALS is so finnicky that onboard tech support is required, so EMALS-equipped ships have a team of civilian support techs aboard to support it. ICCALS had an unsolvable problem with producing consistent end speeds until solid state electronically-controlled fuel injection became available.

C-13 Steam Catapult Aircraft Launch System
Thermodynamic analysis of the C-13-1 steam catapult for aircraft launching from an aircraft carrier

1,389MJ of steam energy is stored for the C-13 aircraft catapult launch system, and about 6.84% gets converted to mechanical work by the steam piston during the launch stroke, which delivers 95MJ of energy to the aircraft being launched. Steam is about 5% to perhaps 10% efficient using more modern materials and higher temperatures and pressures than a C-13. The C-13-2 steam powered catapult launch system became the ultimate expression of steam catapult technology, and was later adopted by the French Navy as well. It's a highly refined system developed and proven over many decades of faithful service, though it has not been without its problems.

Internal Combustion Carrier Aircraft Launch System
Internal Combustion Carrier Aircraft Launch System Background
Back in the 1990s, the US Navy actively pursued ICCALS (Internal Combustion Carrier Aircraft Launch System) before EMALS became "the way of the future". ICCALS was similar to a mortar or grenade launcher "gun tube" that combusted a small amount of fuel and air in a highly confined "charge cup", similar to a 40mm grenade launcher, in conjunction with injected water to produce expanding hot gases and steam, to provide both "soft launch" like EMALS, as well as more total launch energy than steam alone or EMALS, about double what EMALS was projected to provide in the same form factor that the C-13 and EMALS flight deck mounted equipment occupies, at an overall efficiency between steam and EMALS, with much lower "top weight" (the weight of all launch system equipment sitting above the waterline) when compared to either system.

All kinds of combustibles were initially experimented with, starting with gun powder from blank 5 inch gun propellant charges in battleship aircraft catapults long before WWII started, moving on to de-natured explosives now used as monopropellants for satellites, such as HAN and other Ammonia-based compounds and storable but toxic oxidizers, but eventually kerosene and Oxygen were used, because aircraft carriers equipped with jet aircraft store large quantities of JP5 and LOX plants aboard ship.

Modern compression ignition internal combustion engines based upon pistons can be up to 50% efficient, but I would bank on 35% overall efficiency, which corresponds with the efficiency of a well-designed large caliber gun like an artillery piece. Increasing bore diameter relative to bore length makes a gun more efficient at converting combusted propellants into mechanical power.

ICCALS reduced ship-destabilizing top weight associated with the aircraft catapult gear by 380 tons over all 4 C-13s cats and 500 tons over all 4 EMALS cats. EMALS is overall lighter and more compact than steam catapults, but not where it counts- some 50ft to 80ft above the waterline in the case of aircraft carrier catapults. This top weight issue required a major redesign of the Ford class to accommodate EMALS, when compared to the Nimitz class. In practice, this meant using expensive and difficult-to-weld HY-100 steel to provide the necessary strength while keeping top weight in check, to retain the stability of the Nimitz class. From the Forrestal class to the Nimitz class, all other aircraft carriers used HY-80 steel, which is much cheaper because it's much easier to weld and there is less of an issue with weld embrittlement and cracking.

Electro-Magnetic Aircraft Launch System
EMALS stores 484MJ of total electrical energy and delivers up to 121MJ per launch stroke. The stored electrical energy imparted by EMALS is consumed from 4 flywheels spun-up using electrical power from the onboard nuclear reactors, and is sufficient to produce an end-speed of 130 knots (149.5mph) for a 100,000lb aircraft in about 94m, same as the C-13-2 steam catapult. This is a 27.5% greater energy delivery than the C-13-2 steam catapult, in roughly the same form factor. Linear electric motors, such as EMALS, are only about 50% efficient, unlike much more efficient rotating electric motors. In theory, EMALS can allow for more rapid launches. In actual practice, it takes a certain number of seconds for the plane handling crew to direct the pilot onto the cat, connect the tow bar to the cat, complete a last second control system check on the aircraft, run the engines up to full power, and then have the shooter launch the plane.

For comparison purposes, the 121MJ provided by EMALS is nearly identical to the total energy content contained in 1 gallon of gasoline.

In the reports listed below, 1 "cycle" is 1 launch stroke or 1 arrested landing or 1 lift of aircraft ordnance to the flight deck to arm a jet.

MCBCF = Mean Cycles Between Component Failure
MCBOMF = Mean Cycles Between Operational Mission Failure (the electrical aircraft catapult, arresting gear, or weapons elevator equipment fails in some way to do what it was designed to do)

2019:
https://www.dote.osd.mil/Portals/97/pub … 105641-303

EMALS: Absent a major redesign, it is unlikely EMALS will be capable of meeting the requirement of 4,166 MCBCF.
AAG: The requirement is an MCBOMF of 16,500.

2024:
https://s3.documentcloud.org/documents/ … 2-2024.pdf

EMALS: During FY23, DOT&E observed EMALS reliability remained consistent with recent developmental test (460 MCBOMF in FY21 and 614 MCBOMF in FY22). Despite engineering upgrades to hardware and software, reliability has not appreciably changed from prior years and reliance on off-ship technical support remains a challenge.

AAG: During FY23, DOT&E observed EMALS reliability remained consistent with recent developmental test (460 MCBOMF in FY21 and 614 MCBOMF in FY22). Despite engineering upgrades to hardware and software, reliability has not appreciably changed from prior years and reliance on off-ship technical support remains a challenge.

AWE: The AWEs met operational mission needs during these underway periods, but preliminary data suggest AWE is unlikely to meet its operational availability requirement of 99.7 percent. Of note, the crew is reliant on off-ship technical support for correction of hardware and software failures. As of the end of COMPTUEX, the ship had conducted 23,042 total AWE cycles. The Navy has yet to build and transfer ordnance to the flight deck at combat-representative rates.

According to available reports, as of 2024, there was a 70% chance of EMALS functioning as desired throughout any given day. Availability rates have not meaningfully improved since the system was first installed on the Ford class, and are not projected to significantly improve with experience, absent a major system redesign.

I would opine that the reason China's Fujian class carrier and her sister ship remain prototypes, much like the Ford class and her sister ships, is the fundamental unreliability of the prototype-quality installed electrical equipment, which could theoretically be as reliable as steam with far less maintenance, but thus far has not proven nearly as reliable as steam and hydraulics in actual service.

If MJ/kg improved by a factor of 10 for flywheels or super capacitors, then EMALS deployment would be far less objectionable, as we would see a net benefit in terms of top weight, and therefore have far greater incentive to figure out how to make EMALS / AAG / AWE work reliably. The launch rails and flywheels, to my knowledge, have not been particularly problematic, but the power electronics are subjected to a brutal maritime environment. Any practical rocket launch system will also be located right next to the edge of a coastline, thus subjected to a similarly hostile operating environment. A ship on the open ocean adds vibration and twisting / bending forces to the list of confounding factors affecting overall system reliability and maintenance requirements.

Steam vs Electricity vs Combustion
EMALS and ICCALS both have great potential, but not in their current design iterations, and the quantity of energy saved by EMALS over steam has not been commensurate with its extreme development cost, presently $1.3B and counting, since it's still not as reliable as steam. Money is still money. Time is the one resource you never get back. When you waste time and intellectual effort on a technology that's fundamentally unreliable in the operating environment it will be subjected to, there's nothing you can do to recover that lost time. This is life or death in a war, but it's still profit or bankruptcy in business.

There is no crystal clear picture on whether or not any of these competing technologies will actually save time / money / labor over the others. Thus far, EMALS has not saved any labor or money over steam catapults. Theory frequently doesn't match-up very well with reality. Cost and labor centers have moved around a bit, but that's not indicative of an actual improvement.

The giant reactors aboard Ford produce near-endless quantities of steam to work with, much as a large solar thermal power plant will produce steam until the cows come home, and at night if the power plant has molten salt energy storage. These thermal energy storage systems do not appreciably degrade over time, unlike power electronics, and they can be repaired far more easily than electronics when they do fail. Electronics and electrical devices are seldom repaired, and almost always entirely replaced. I can't imagine that frequent replacement of major subsystem components is part of a viable business model when alternatives exist. It's more like something a government would do when working with someone else's money.

Steam is agnostic on its input energy source. Apart from photovoltaics which directly produce a minor fraction of the electricity that modern society is now entirely dependent upon (try telling a hospital they can't have their electricity and see how that conversation goes), heat sources (solar thermal, nuclear thermal, combustion) do not directly produce electricity. I'm aware of MHD generators, but nobody uses those. By definition of what you're doing, any conversion of thermal power to electricity will most likely be an inefficient / high-loss process. You convert 1/3 to 1/2 of the input thermal energy out as electricity, and that congruent with current technological reality. EMALS efficiency in actual practice is no better than combustion. 60% of the energy the reactor produces is lost during conversion to electrical power, and then 50% of the generated electrical power is lost during operation of the catapult. Despite those losses, EMALS is still more efficient than direct steam, but total efficiency matching a carbureted piston engine, with far greater total complexity and cost, is nothing to write home about.

Steam has exceptionally well-proven reliability and a centuries-old technological heritage. We know how to use it reliably, only low-cost and common materials are required to use it, and any mechanical engineer worthy of that title has at least passing familiarity with the technology. 25 years into the 21st century, the majority of the power in today's world is still provided by over-glorified steam kettles. Water is quite literally everywhere on Earth, but most importantly water is readily available in endless quantities where space launches actually take place.

Sourcing water for a coastal steam-driven catapult launch system is not a giant logistics question mark. If you have a pump, the water is there for the taking. You don't need electrical or electronic parts and tech support, you don't have to concern yourself with whether or not your fuel delivery truck driver is going on strike, and the Sun is most definitely coming up tomorrow. In other words, the power source (the Sun) and the power delivery medium (steam) are pretty much a given. As the Navy has proven over many decades, you can take a kid out of high school, train him for a few months at most, and then he can operate a steam catapult without issue in a highly confined environment. Businesses like "sure things", because they can develop successful business models on concepts that are all but iron-clad in how they function.

If electricity was sourced from photovoltaics and EMALS reliability improved to the point that we didn't need tech support onsite at all times, then total efficiency is better than steam. The issue seems to be achieving that reliability.

Combustion has better total energy delivery potential, but at the cost of the fuel and oxidizer for the launch, plus cleaning out the gun if any fuel besides natural gas is used. Launching 1,000 short tons with an end-speed of 130 knots will require about 60 gallons of fuel, plus oxidizer, at 33% overall efficiency. For an end-speed 5X faster, or 650 knots, only 17 knots shy of breaking Mach 1 at sea level, ignoring aerodynamic drag, which will be very significant for a vehicle of that size, requires 300 gallons of fuel. That's probably doable, but you still have to maintain the equipment to mix the fuel and oxidizer, and your feed system has to be near-perfect to produce the exact correct end speed. The timing of each shot and the end speed does need to be precise, as most rocket launch windows are timed to the second to arrive at a precise location in orbit near another vehicle already in orbit. If you launch once per hour, then 7,200 gallons of additional fuel per day is very significant. You need a natural gas pipeline or tanker cars, because fuel trucks get expensive pretty fast, and storing tens of thousands of gallons of additional fuel and oxidizer is also expensive and also requires more capital outlay to pass all the regulations, inspections, site design requirements for fuel storage, etc. The entire idea here is to require less of that, because fuel and oxidizer rapidly become your greatest expenses when you operate like an airline transport service.

All 3 technologies clearly do work, but only steam catapults can be built without further fundamental tech development, which is a major impediment to a company that wants to be in the launch business, rather than the aircraft catapult tech development business.

Calliban · 2025-01-28 13:40:21

Kbd512 makes a convincing case for steam over alternatives.

The pressures involved do not need to be great. Starship upper stage weighs 1700 tonnes fully fuelled and is 9m in diameter. If the ship is mounted on a sabot some 10m in diameter, that amounts to a mass of 21.65 tonnes per square metre. Accelerating at 7g and adding the force of gravity, requires a base driving pressure of 17.2bar. Say 20bar (2MPa) when the weight of the sabot is included. The saturation temperature of water at 2MPa is 215°C. That is easily achievable using a trough solar collector.
https://www.engineeringtoolbox.com/wate … d_599.html

The rms speed of water molecules at 215°C is 822m/s. So steam at 215°C will have no problem accelerating a rocket to circa 300m/s.
https://www.vcalc.com/wiki/pro/Root-mean-square+Speed

Potential problems:

1) Vibration: Anyone who has stood near a boiling kettle knows about that. Bubbles cause vibration when they burst. Could that be a problem for a rocket? Maybe we let the water boil in an external vessel and pass the saturated steam through a rock bed to dry it.
2) Barrel corrosion. The best material to use for the barrel is probably low alloy steel. This has excellent ductility, is easy to weld and doesn't suffer from heat sensitisation. But it will corrode in saturated steam. Maybe use a liner of some kind?
3) The sabot needs to be reusable. Do we attempt to recover it via parachute or do we rapidly decelerate it at the top of the barrel?
4) Will noise be a problem? If the gun is pointing upward, then the shockwave will disperse upward. So the barrel noise should be bounded by the noise from rocket engines. We could put a suppressor of sorts around the top of the barrel to absorb as much nouse as possible.
5) We want to be able to launch 24/7, 365 days per year. Will seasonal variability of solar thermal heat be a problem? What is the best solution to this problem?

The steam temperature needed is beneath the critical point of water. This means we can store the steam as saturated liquid in a steam drum. That makes operating the cannon easier, as the steam drum can be slowly recharged with hot saturated water between shots. If the drum draws its heat from a molten salt thermal storage tank, then 24 hour operation should be straight forward. We could supplement solar heat by burning natural gas or some other fuel in winter.
******

Additional: On Mars, we could build a similar device using compressed CO2. Even at 0°C, CO2 has a rms speed of 394m/s. We can store CO2 as a compressed saturated liquid and allow it to boil in something analogous to a steam drum. At a pressure of 2MPa, the saturation temperature of CO2 is -20°C. We can boil the CO2 using liquid water as our heat storage material, instead of molten salt. So our solar collector only needs to operate at about 0°C. Or we can use powerplant waste heat to drive the cannon. This could be a very efficient way of launching payloads on Mars. Compressing the CO2 back into liquid is very energy cheap at Martian nighttime temperature. Any spare electrical energy from our base power supply can do that.

Last edited by Calliban (2025-01-28 14:34:32)

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#1 2014-02-04 17:18:57

Solar Thermal for Ground Launch

#2 2014-02-05 03:43:47

Re: Solar Thermal for Ground Launch

#3 2014-02-05 12:18:25

Re: Solar Thermal for Ground Launch

#4 2014-03-09 15:44:32

Re: Solar Thermal for Ground Launch

#5 2014-03-09 17:42:43

Re: Solar Thermal for Ground Launch

#6 2014-03-09 20:45:18

Re: Solar Thermal for Ground Launch

#7 2014-03-10 16:20:50

Re: Solar Thermal for Ground Launch

#8 2025-01-26 11:28:49

Re: Solar Thermal for Ground Launch

#9 2025-01-27 09:59:09

Re: Solar Thermal for Ground Launch

#10 2025-01-28 13:05:52

Re: Solar Thermal for Ground Launch

#11 2025-01-28 13:40:21

Re: Solar Thermal for Ground Launch

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