America's Hunting Eyes in the Sky (A Version of the Future)

Thursday, April 7, 2044

Watch out world, because the sky above you just got a lot more watchful.  On April 5th, a US Air Force spokesperson officially confirmed that the MIL-Cast satellite network is more than a communications and observation platform, but is also a space-based weapons platform, as suggested in our 2039 Article "Secrets of MIL-Cast"

"Good morning everyone, I am here to announce that as of 0200 this morning the robotic geoengineering platform Jotunn has ceased operation after illegally entering the waters of South Georgia Island.  At the request of the UN Climate council and with permission from the British government US forces deployed 3 Falcon Earth Observation Drones to perform a kinetic observation of the Jotunn...."

When asked why the Air Force was finally acknowledging the offensive capabilities of the MIL-Cast General O'Neill was rather blunt.  "We're running out of the darn things, every other week we need to 'kinetically observe' some bad guys and hiding the launches was too much of a hassle"......

From our research, we believe there are between 20 and 30 thousand Falcon satellites in the MIL-Cast network.  With a mass of about 50 kgs, they share many characteristics with other atmosphere skimming communication/observation satellites used by civilian firms.  Most experts who were willing to go on the record believe the biggest differentiator for the spacecraft comes in the way they are designed to re-enter the atmosphere.  Civilian satellites are designed to safely break apart when they enter the atmosphere. The Falcon appears to be able to precisely control entry depending on the mission when the craft reaches its end of life it will disintegrate like a shooting star, as many Americans saw in the 2040 Seatle Summer Olympics opening ceremony.  The secondary re-entry method allows 10-20 kg of the vehicle to strike a target with over 100 megajoules of kinetic energy.  

Would you like to know more?

This article is a continuation of my post "Looking at the Future of Low Earth Orbit".  Basically, the idea is that a future government might use really low orbiting satellites as more than just communications/observation platforms.  As satellites get cheaper and cheaper to launch it isn't crazy to imagine that a large nation-state like the US would look for additional ways to weaponize space.  The idea of dropping heavy objects from space as a weapon has been around since the 1950s.  The proposed Falcon above would be a much smaller vehicle than what the Air Force has investigated previously.  

The 100 Megajoules was based on the Wikipedia entry on how much kinetic energy orbiting objects have.  To put things in perspective 100 MJ of energy is the equivalent of about 23kg (52.5 ish lbs) of TNT.  Depending on where the Falcon hits the explosive energy would be enough to either really mess up your day or to just really really surprise you.

For those of us concerned about peace one thing to find comfort in this suggested weapon is that at this time I have no good idea on how you would actually make a satellite that goes magically from safely breaking up to something that will stay together at speeds high enough to do real damage.

I hope this was interesting, questions, comments, and general feedback are welcome

Fricken Rockets Getting Boosted by Fricken Lasers (oh its a bit longer now)

In part 1 of Fricken Rockets Getting Boosted by Fricken Lasers we got some background on the concept of laser enhanced rockets.  (If you haven't read it yet, I would suggest clicking here first) 

Powering our Saturn 5's electric turbopumps is incredibly energy-intensive, requiring almost as much energy as the propellers on a nuclear carrier.*  The variable that most directly impacts our turbopump's energy demand is the flow rate of the engines, the flow rate for the engines is dependent on the mass of the spacecraft.  The bigger our spaceship, the more flow rate we need to keep the engines fed.  The Saturn 5 was capable of transporting 140,000 kg to Low Earth Orbit for sake of comparison a SpaceX Falcon 9 Full Thrust is capable of transporting 22,800 kg to the same orbit**.  The Falcon 9 Full Thrust uses its 9 Merlin Engines to achieve about 16.3% of the payload capacity of the Saturn 5.  Each Merlin Engine has a massive turbopump supplying 7.5 MW of pumping capacity, meaning that the Falcon 9 FT needs about 67.5 MW of total pumping capacity.  Observant readers, with probably insane levels of recall, might note that the Saturn 5's first stage pump requirements totaled 205 MW when we compare this to the Falcon 9 FT's 67.5 MW turbopump power we see that the Falcon has about 32.9% the total pump capacity of the Saturn 5.  What the Falcon 9 has over the Saturn 5 in our energy concerns is that there is relatively more surface area for our lasers.

For our Saturn 5 calculations, we assumed that about half of the area of the first stage would be devoted to our power receivers, giving the lasers about 200 square meters of effective area to target.  A Falcon 9 first stage is 42.6 meters tall and 3.6 meters in diameter, that means that if we covered the body of the first stage with collectors our lasers could reasonably expect an effective target area of about 75 square meters.  This surface area is fantastic news laser boosted rockets while 75 meters is only about 38% of the area of the Saturn 5, the energy demand for the Falcon's pumps is only 32.9% of what the Saturn 5 needed.  Using our 40% conversion efficiency, we can estimate that the rocket will need to receive 168.75 MW  of energy from the lasers (67.5MW/0.4).  The average peak flux of energy on the rocket would be 2.25 MW/m^2, or about 12% less than what the Saturn 5's receivers would need to handle. 

Scaling down to the Electron rocket the math gets even more interesting.  At 17 meters in total height and 1.2 meters in diameter, we can conservatively estimate the ability to have 6 square meters of receivers.  These 6 square meters will need to supply up to 1 MW of power to the pumps, giving us 2.5 MW of laser energy needing to get to the rocket (1MW/0/4).  For the Electron rocket the panels would only need to handle 416 kW/m^2 of flux (2.5MW/6m^2).  While this isn't a small amount of energy, it is way more manageable than what would be needed for larger rocket launches.

By modeling three different sizes of rockets we can see that the smaller the rocket the smaller the energy overall needed to power the turbopumps.  A combination of needing less energy for the turbopumps in tandem with increases with relative surface area gives an exciting opening for developing laser enhanced rockets, start small and build bigger as technology improves.*(3)

Developing laser Enhanced Rockets might follow a timeline something like this

Step 1
Wireless power transfer testing.  Create a competition where teams are challenged on their ability to have a combination system capable of transferring Energy densities of over 400 kW/m^2 without exceeding design envelope for first stage rocket body simulant

Step 2
Wireless power transfer testing with moving targets
Winners of Step 1 and additional applicants will compete to wireless beam energy at sample liquid fuel rockets.  These rockets will still use traditional turbo-pumps, teams are judged on their ability to continuously supply a set energy intensity to the rocket.

Step 3
Small Scale Pump testing
Competing institutions will be challenged to build liquid fuel powered sounding rockets with electric turbopumps.  Scoring parameters might include factoring what percentage of power for the turbopump came from wireless energy sources.

Step 4
Moving into commercial development of electric turbopumps

Step 5 Launch a spacecraft where some of the power needed for launch comes from wireless energy


Step N
Next-generation laser enhanced competition, as energy densities of long range wireless power transfer increase to certain pre-determined values, organizations like NASA and DARPA have competitions where teams compete on their ability to propel rockets where some amount of direct thrust comes from heat provided by lasers.

 (at this point I ramble a bit, feel free to keep reading, but I won't judge if your eyes just glaze over and you just decide to read something else)

Developing a laser enhanced rocket system will not be an easy undertaking, while the abstract principle is straightforward there are many risks to commercialization.

Cost of developing the laser platform will be the biggest challenge, our world is rife with innovations that came too late after market forces chose a solution.*(4)  Theoretically, a laser enhanced rocket should be cheaper than a more conventional design in the real world this is not a guarantee.  Getting laser enhanced rockets to the point where they can compete on cost will not be easy.

A best-case development scenario for laser enhanced rockets would come from a partnership of multiple space launch companies agreeing to implement the technologies mentioned above.  Each partner organization would share the cost of the laser power base stations maintenance and upkeep. 

Realistically for laser enhanced rockets to become a mainstream innovation the number of launches will need to increase drastically.  Frustratingly for futurists, we need a large volume of launches from the same general geographic vicinity and for those launches to have a fairly similar first stage flight path.  The more variation in launches the less useful our laser platforms would be (or more expensive as the lasers would need to cover more area).  These realizations should not be treated as an absolute negative.  For much of the commercial sector flexibility in space-craft orbits is incredibly useful, but for projects like sending missions beyond the Earth-Moon system, a standardized orbit isn't necessarily a bad thing.  A standardized orbit and rendezvous location would allow for the development of an orbital dry dock facility.  At this drydock fuel and materials could be stockpiled for future missions.  Refueling and assembling in orbit could allow for much more flexible deep space missions, instead of requiring the first missions to Mars to produce all of their return fuel on Mars mission planners could take advantage of fuel stockpiles that built up as secondary payloads for other launches.

Another approach to improve the utility of laser enhanced rockets in the early stages is by creating an open standard booster stage and docking mechanism.  These open standard boosters could supply additional early-stage power with a more narrowly defined flight path than a full first stage. 

I hope you found this idea interesting, I know its a complicated topic, feedback and questions are welcomed.

*according to the Wikipedia article linked above, a Nimitz carrier's nuclear powerplant supplies about 260 MW of power to the propellers, vs our 205 MW of pumping power (some might say 78.8% isn't almost but I'm gonna, because finding analogous power requirements was wasting way too much time)

**okay so not like perfectly exact, this is because the Saturn 5 article lists its lift capacity for getting to an orbit of 170 km with an inclination of 30 degrees, on the flip side the Falcon 9 Full Thrust just lists low earth orbit and an inclination of 28.5 degrees (where low earth orbit isn't well-bounded) for those who want to crunch the numbers in greater detail to minimize the confusion on the comparison please feel free to let me know.  That being said these numbers probably get us in the ballpark.

*(3)  we shouldn't ignore the fact that turbopumps do in fact get more power-efficient as they get bigger.  The Electron can only get about 200 kg into orbit less than 1% of what a Falcon 9 FT can get into orbit, at the same time, the Electron's pumps need about 1.48% of the power than the Falcon 9 does.  Basically, Falcon 9's can move 48% more cargo per unit of pumping power (not a useful actual rubric but interesting)

*(4)  this is along the lines of BetaMax vs VHS or BluRay vs HDDVD, not some kind of conspiracy

*(5)  we are going to assume these panels are designed to be readily added to a rocket and have the appropriate mass properties

The best-case scenario for a country like the United States would be something like this. 

The US Airforce in a continuing desire to increase launch cadence declares that launches must meet certain cost performance goals, to that end they offer affordable access to an Air Force owned power transfer station and a partnering business would supply the necessary panels*(5) to capture the energy required for launching.  The added weight of these panels and the associated electrical sub-systems is offset by the improved fuel efficiency as more rocket fuel can be used to actually propel the spacecraft.

Without a government backing laser enhanced rockets, we are unlikely to see this technology hitting mainstream uses.  The aerospace industry has sunk billions of dollars developing the rocket technology they use

Fricken Rockets Getting Boosted by Fricken Lasers

(now for part 2 of "The Polls Are In")

At its most basic, rocket science sounds really easy, just get something going fast enough that it will leave a planet's atmosphere.  Once you start accounting for things like cost efficiency it starts getting harder.  Over the past 20 years, the barriers to launching into orbit have dropped dramatically, with companies like Blue Origin, Rocket Labs, and SpaceX competing against traditional launch firms, prices have started to come down.  Space tourism is still out of reach for much of the world's population, but for businesses that need satellites affordably transported into orbit, times have never been better.  A key driver in lowering the barrier of entry to launching a rocket comes from a combination of being able to launch smaller/lighter satellites with more affordable rockets themselves.  

There are several ways to make a rocket more affordable, better manufacturing techniques, reusing components, large volumes of production, and making a rocket's engines more efficient.  For each of these cost-saving techniques, there are countless proposed approaches to make improvements.  Making rocket engines more efficient is an incredibly complicated challenge, where engineers must account for the chemical reaction creating thrust, the heat produced by the engine, moving fuel fast enough to keep everything moving, and countless other subtle variables.  One possible way to enhance engine efficiency is to make the rocket's exhaust hotter, hotter exhaust equals more thrust for a given amount of fuel*.  Scientists Arthur Kantrowitz and Wolfgang Moekel realized that the boost of higher exhaust temperatures didn't necessarily have to come from the reaction of rocket fuel and its oxidizer.  In the 1970's they proposed using lasers to enhance the exhaust temperature of a rocket.  Instead of having to carry rocket fuel and liquid oxygen, these laser enhanced rockets would only need to carry a propellent, like water.  

Laser thermal rockets would benefit from having a relatively safe first stage if engineers noticed any problems with the rocket, they could simply turn off the lasers supplying the heat power and drastically reduce the risks faced by those near the launch site.  This boost to safety comes with a cost, having enough powerful lasers to heat water to high enough temperatures to propel a decent sized rocket would be incredibly capital expensive, consequently, laser thermal rockets have been relegated to small scale academic research.  What laser enhanced rockets need is a path from academia to industrial use.  Enter the electric turbopump.

Turbopumps are what you think they are super powerful pumps inside of rockets that help to make sure that there is always the right amount and mix of fuel and oxidizer.  For the Saturn 5, these turbopumps were truly massive, producing 41 MW of power (55,000 brake horsepower) to move 58,560 liters (15,471 gallons) of rocket fuel and 93,920 liters (24,811 gallons) of liquid oxygen.  To generate all this power it was necessary for engineers to make a complicated design that diverted some of the energy of the rocket motor to powering the turbopump.  The aerospace company Rocket Labs has recently broken with industry traditions and developed the Rutherford Engine a rocket engine that uses a battery-powered turbopump.  This innovation of a battery-powered turbopump is possible due in part to improvements in battery energy density.  While development is very exciting for the small satellite launch community, the energy requirements of fluid pumping for larger rockets make this innovation unlikely to scale if batteries are used as the energy source for the turbopump.  

Larger rockets would need a lot of power to run their turbopumps.  For the Saturn 5's first stage you have 5 engines needing 41 MW of pumping power each.  Each of these engines will need to run for 168 seconds, and assuming a safety margin of 12 extra seconds of burn time, let's say the pumps need to be able to run for 180 seconds (3 minutes).  We also need to assume that powering the turbopumps is only 90% efficient, meaning the electrical systems for each turbopump would need to supply 45.6 MW of power.  Putting all our variables together we see that our 5 engines, consuming 45.6 MW each, for 180 seconds would require 41.04 GJ** of energy.  That's a lot of energy, to put things in comparison a Tesla Model 3 with the largest battery option has a 75 kWhr battery which holds about 270 MJ (0.27 GJ).  Our new Saturn 5 would need 152 Tesla Model 3 battery packs to run its turbopumps for all of 3 minutes.  It gets more complicated, traditional batteries have a maximum discharge rate; it would be unlikely that we could design a battery pack that would be able to go from 100% charge to nothing in only 3 minutes***.

Instead of batteries what if our turbopumps got most of the electricity from power wirelessly sent from base stations?  

Keeping our requirements from the previous section of 5 engines each needing 41 MW of pumping output running for a period of up to 180 seconds, but now we have a different consideration make sure we can safely transmit sufficient power to run the pumps while keeping the system's weight to less than that of using batteries****.  The two most popular long-distance/low loss means of transmitting energy wirelessly are lasers and microwaves.  Converting laser light into electricity is currently estimated to have an efficiency from 40-50+% that means that if your system needs 1 watt of power, your laser will need to have an output of about 2 watts.  Documentation on using microwaves to transmit DC power has been harder to come by, but values as high as 95% are listed on Wikipedia.  Conversion efficiency is important from a heat management standpoint, the less efficient the conversion process, the more heat the vehicle's design will need to account for.  

Beyond conversion efficiency, engineers would need to account for the maximum flux the receivers can handle.  Flux is a measure in Watts per Square meter of how much energy an object can handle, for example, certain plants are adapted to grow in shade, they are happiest when they get soft indirect light if the plant gets too sunlight, they could end up damaged.  For something like a Saturn 5 to get its 205 MW of power to the turbopumps, our 40% efficient panels would need to be absorbing over 512.5 MW of laser energy*(5).  The Saturn 5's first stage was 41 meters tall and 10 meters in diameter, we are going to assume at any given moment about 200 square meters of the first stage will be able to absorb our laser's energy.  To achieve our model's requirements our panels would need to be able to handle 2.5625 MW/m^2, for sake of comparison sunlight in space produces about 1360 watts/m^2.  The power receivers would need to handle 2000x more energy than sunlight.  

We should keep in mind that the estimated power hitting the receiver assumes that the lasers are targeting a flat surface.  A more detailed analysis would factor in the curvature of the rocket, where only a small percentage would experience the 2.56+MW/m^2 of peak laser radiant flux.

At this point this post is already way longer than I originally planned, it turns out rocket science is hard and I hadn't done any actual deep analysis until I started writing and I would like to give this concept the analysis I feel it deserves.  What to expect in the next post.

A rant about the square cubed law, the Saturn 5 has less area per unit mass than say a Falcon 9 or an Electron rocket, this means the lasers need to power the Saturn 5 pumps would need to have a much higher energy density when hitting the side of the rocket.  The 9 Merlin Engines on a Falcon 9 have 7.5 MW turbopumps.  The Electron Rocket from Rocket Labs has 9 Rutherford Engines, with each engine requiring roughly 75 kW to power their turbopumps (37 kW for oxygen, 37 kW for fuel)

A proposed timeline for how commercialization might go (start small and build)

Thoughts on cost efficacy of this proposal (it would depend on many market forces and how long investors are willing to amortize costs)

I hope this was an interesting start

*there are probably some exceptions to high exhaust temperature vs produced thrust, but from this rocketry 101 article from NASA it appears this is generally the case https://www.grc.nasa.gov/WWW/K-12/rocket/rktthsum.html

**GJ is shorthand for gigajoule or 1 billion joules, lots of energy MJ is a megajoule 1 million joules

***This is to acknowledge that supercapacitors are a thing, while they have a lower energy density, they can discharge that energy much faster than a traditional battery can.  So yes, they are a thing, and yes, they might be part of the solution, but giving supercapacitors their proper depth would make this article way way too long

**** I mean technically the most important comparison is competitiveness with traditional turbopump launches, but c'mon, do you guys want a book?  (seriously if you do let me know)

*(5) this is just the laser hitting the spacecraft, depending on energy lost to the atmosphere we could be seeing some really big lasers being needed to get power to the spaceship

*(6)

The Polls Are In

A couple of weeks ago, I asked folks what they wanted from an upcoming post: solar power on farmland, laws about Lunar mining rights, or laser enhanced rockets. The winner is...

A TIE

Solar Power on Farmland and Laser Enhanced Rockets received equal interest. Consequently, I will be doing posts on both. Today we will be looking into making solar power production more symbiotic with farming.

Agrophotovoltaics is a relatively new field of development in the world of renewable energy production. For those of you who are language geeks, you might infer from the name agrivoltaics that it deals with agriculture (farming) and photovoltaics (one of the types of solar electricity energy production). For the rest of you, I hope that this cleared things up. The motivation behind agrivoltaics is relatively straightforward. Traditional commercial-scale solar farms are optimized to do one thing—converting sunlight into electricity. The efficiency of large scale solar farms comes with the trade-off that the land devoted to electricity production can't really be used for anything else*.

As our planet heats up, farmers are faced with the question. What will they do with fields that have climates that no longer match the crops they've grown historically? For many farmers in California, they are making the choice to replace some of their plant-based crops with solar farms. While adding tradition solar capacity to farmland is a great way for these farmers to gain a new source of revenue while reducing water consumption, there are some trade-offs.  

Many traditional solar leases require that farmers sign a 20-year contract—the average life span of a solar farm. For the life of the lease that farmland cannot be used for any other purpose. The 20-year contract is generally considered a good deal for both parties. The farmer has guaranteed lease revenue and the solar company knows that the land will be useful for the operational life of the solar panels. During dry years, where farmers are unable to irrigate all of their lands anyway, the acreage devoted to a solar farm is a boon. Revenue will continue to be earned even if plants don't grow. In wetter years, with good crop prices, farmers may lament the unavailable acreage that could have increased their revenue that season.

Famers who implement agrivoltaic systems on their fields can exchange higher upfront costs for a guarantee that every acre of useable land that they had before installing solar panels is still available for the life of their installation. The risk associated with using agrivoltaics over utility photovoltaics should not be taken lightly. Current published materials indicate that the cost of installing an agrivoltaic to be roughly the same as installing rooftop solar on a home, about $3/watt installed. Depending on how you model the upfront/operational costs of an agrivoltaic system, the cost efficiency for farmers will vary drastically.  

Assuming an installation cost of $2.58/Wac installed (the current low end for electricity installation costs) and using Dr. Ramon Sanchez's solar calculating tool,** we can estimate that farmers and customers would need to buy the electricity wholesale at $0.113/kWhr. The upper bound installation cost of $3.38/Wac would leave us with an estimated wholesale value of $0.148/kWhr. When you consider that the average consumer only spends $0.1332/kWhr on electricity, it becomes more difficult to make a simple recommendation to use agrivoltaics, unless you get clever***. Traditional farming requires a lot of energy in the form of fossil fuels used to move tractors and other equipment, a farmer who embraces local energy production and storage could look at their costs in a very different way. Instead of looking at their solar installation as a way to make money from the sale of electricity on the wholesale market, they could see as a way to reduce the impact on the variability of fuel oil prices.  

Manufacturers are already starting to sell electric tractors. As time goes on, farmers who embrace solar will be able to have a more consistent energy budget for their farm in the form of the mortgage for their solar installation.  

Other potential benefits of an agrivoltaic installation include providing a scaffolding structure for robotic farming technologies. Companies like FarmBot are working hard to make robotically enhanced garden beds that will automatically handle the majority of a garden's lifecycle. The scaffolding structure of the agrivoltaic system could very readily be designed to act as a structural trackway for robotic arms to move across a field, optimizing plant growth while minimizing the number of labor hours needed from humans.  

There is one more idea I wanted to share, but as this article is already rather long, I felt it would be better to give the idea its own post. That being said, the core concept is right below.

• Inflatable algae greenhouse for producing biofuels during the winter months

(I hope you're intrigued, any questions and feedback are welcome)

*There are some options for doing a few other things on commercial solar fields. As an example, you can graze animals off of the grasses that grow around the panels.  

**These calculations were done for San Juan, Puerto Rico (I had some old models from a class project I did last week). For a region with less sunlight, the cost of production would be even higher. We are also assuming a DC to AC conversion efficiency of 82.5%

***If you assume that the agrivoltaic systems are being built to sell electricity wholesale because you need to pay a grid operator to transmit your power to other consumers a lower wholesale cost is important. On the flip side, it is worth noting that the current cost for installing agrivoltaics is heavily impacted by the generally custom nature of the frames used to mount the panels. In theory bulk manufacture of agrivoltaic scaffolds designed to make installation more affordable could lower the effective cost of electricity production.