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Articles by Russell Borogove
Paul Byrne (@theplanetaryguy.com)
Paul Byrne theplanetaryguy.com did:plc:wwbktud2d34ont3frkv73pjo This will never stop blowing my mind. A 12-year sequence of real telescope images of a star 133 lightyears away. And around it, four planets slowly orbiting. Four real exoplanets, each more massive than Jupiter, imaged as they move around their host star. 2026-10-02T02:14:08.162Z Enable JavaScript to use Bluesky. Learn more about Bluesky at bsky.social and atproto.com.
How much bigger could Earth be, before rockets wouldn't work?
$\begingroup$ hint: Apparently the Tsiolkovsky rocket equation does not actually say that you can launch a conventional rocket into orbit around an arbitrarily large and massive body. I'm looking for a number based on scaling the earth radius and maintaining the same average density. Must attain LEO, which also gets faster as the planet grows. Don Pettit's Tyranny mentioned in this nice answer is fun, but does not present enough math. On this Earth, rockets barely work.
Is it legal to steal the American flag from the moon?
48 $\begingroup$ I'm not quite sure whether the question is correctly answered here or whether it belongs to Law Stack Exchange. Assuming I can fly into space, more precisely to the moon and back again. What laws forbid me to collect the American flag (regardless of its condition) or any other object of a space nation and bring it back to earth? Would that be "simple" theft? If the country is important because of its laws, I would like to know from the perspective of the USA, China and Germany.
Will the real Snoopy please stand up?${}^†$ Has the candidate object for Apollo 10 lunar module been publicly identified?
Asked Viewed 472 times $\begingroup$ This tweet seems to suggest that the details will be released only after a mission is planned and funder, or at least $50 million is put in escrow, or a bitcoin wallet is offered, but I am not sure I understand the full story. Frankly if someone said "here's $50 million to develop the mission to prove it's Snoopy" I'd genuinely reply "here's the details for a very worthy charity ..please give it to them" tweet: So here's my challenge ..
How did NASA get the video camera on the Moon to track the LM ascent stage, considering the substantial delay?
20 $\begingroup$ The Moon's distance can be as much as about 406,000 km from Earth. That's a round trip light time of roughly 2 x 406,000 / 300,000 = 2.7 seconds or more, depending on how the signal was relayed to mission control, plus any response time. When the ascent module launched and accelerated vertically, how (the heck) did NASA get the video camera on the Moon to track it correctly several seconds in the future?
Were there any issues with wind on rockets / shuttle?
During the STS-115 launch countdown a wind direction change occurred at ~15,000 feet (15 ft/s tailwind to 10 ft/s headwind) over a period of roughly an hour. Since the first stage trajectory had been designed using the original winds, this resulted in a reduction in dynamic pressure margin. A special assessment was done using the L-1:10 winds measurement and dynamic pressure was predicted to be at ~100.2% of the limit where 100.5% would have been a "no-go" call.
When the ISS moves, do the astronauts feel it?
The rate of change is pretty low with pretty low acceleration. (Consider the mass of the ISS(370,000 kilos) and the output of the Progress booster engines at just under 3000N of thrust). One interesting experiment to consider is something you can try on a train that has open gangways. I.e. The cars are connected and it is one long tube. Stand at either the front or back of the train. When the train starts up from a station, pay attention to the breeze. At rest, the air inside is at rest.
How large a body could a probe with ion engines land on and launch from?
Researching small asteroids up close by use of robotic probes seems like an appealing near-future mission. One option is a sample return mission that goes to one large body, another is a mission where a number of smaller bodies are visited over time. In either case, the thing is to land, then launch again, and ultimately return to Earth with samples, perhaps even drilled core samples.
Why are rocket mass on the launch pad and payload mass to LEO not strongly correlated?
What explains the relation between how much a launcher weights on the launch pad, and how much mass it can lift to orbit? I had expected that more payload requires more fuel to be launched and that a launcher is built around that fuel mass. I'm surprised to see that these two measures are just weakly correlated. The data I use here is indeed sloppy but it can't be that much off, or can it? (I'm getting suspicious).
What are the criteria to put the oxygen tank above or below the fuel tank for a given stage of a rocket?
Tanks can be arranged in a variety of ways and the tank design can be used to exercise some control over the change in the location of the center of gravity. As in all aerospace development, the booster tank arrangement is a design tradeoff. Minimization of structural weight and overall system cost would be traded off. I seriously doubt that thermal considerations play a major role in the arrangement of the tanks; the booster is only fueled for a short time and the flight time is even shorter.
After a trans-Mars transfer, what is the direction of the rotation of the orbit around Mars?
Either prograde or retrograde entry is easy to achieve; the choice of trans-Mars trajectory can put the spacecraft slightly ahead of Mars' position at arrival (yielding retrograde orbit) or slightly behind (prograde). A midcourse correction maneuver of about 1 m/s ∆v can make the difference. For Apollo, the retrograde entry was, I think, needed for the free return option. Prograde approach would have sped the spacecraft up on flyby and made for a very long trip home.
Why is there so much variation in the number of engines on launchers?
Designing and building small, low-thrust engines is generally easier than designing and building large, high-thrust engines, but the larger engines may be more efficient. The more engines you have, the more likely one or more are to fail in any given launch. Once you have more than 5 or so, you may be able to continue on if one fails (depending on which engine, and at point in the ascent it happens).
Were the Apollo 11 astronauts aware of any parts of the Luna 15 mission?
Yes, they were aware. According to the Apollo transcript, Luna 15 was prominent in the daily news items that mission control shared with the crew. In the transcript, timestamps are day/hour/minute/second; speakers are: 23 hours into the mission (i.e. on July 17), we have the first mention of Luna 15: 00 23 14 09 CC 11, this is Houston. If you are interested in the morning news, I have a summary here from PAO. Over. 00 23 14 20 CDR Okay. We're all listening. 00 23 14 23 CC Okay.
Has in-space refueling been done?
Before the Apollo program committed to the lunar orbit rendezvous mode, one of the Earth orbit rendezvous proposals involved launching two Saturn Vs, one with the Apollo spacecraft and large lunar descent stage, with little or no oxidizer in the S-IVB translunar stage, and the second carrying a large LOX tank. The two would rendezvous in Earth orbit and transfer LOX before TLI.
How fast does Roche limit disintegration proceed?
The Roche limit is just the distance from Jupiter at which the "stretching" of the object by Jupiter's tidal force exceeds the internal gravitational force of the object. So certainly in some sense yes, 35 minutes is long enough for the Earth to "break up".
How much faster (or slower) would it be for a new probe to reach Pluto?
In the absence of a gravity assist, the most fuel-efficient route from Earth to Pluto is approximately a 45-year journey. Bringing that down to 9 years already represents a large investment in propulsion fuel; New Horizons set the record for the highest launch speed of a human-made object from Earth (~16 km/s); the Jupiter flyby increased its speed by another ~4 km/s.
Why are Rocket engines at the base of the rocket?
..what reason is there for having the engine at the bottom, .. Heat. Rocket exhaust is very hot, therefore the rocket exhaust would have to come out of the engine and past the long fuel tanks (which often contain fuel or oxidizer at 'cryonic temperatures') before the rocket is safe from them.1 Fuel flow. It is harder to pump fuel up to a rocket engine (against both gravity and the acceleration of the rocket), than to allow the fuel to flow down to the engine. Control.
Why do Soyuz landings often occur north and northeast of the target location
Soyuz descent module re-entry flight is piloted (one of two modes AUS/computer or RUS/manual), using 8 thrusters, toward the Kazakhstan landing site. The ballistic re-entry occurs only when the other modes are inoperative (e.g. TMA-11) or in case of an urgent departure from the ISS. With a controlled descent, the actual landing location should be equally distributed around the target point, but it seems most of the landings occur N or NE of it.
Why do Soyuz landings often occur North-East of the target location
Soyuz descent module re-entry flight is piloted (one of two modes AUS/computer or RUS/manual), using 8 thrusters, toward the Kazakhstan landing site. The ballistic re-entry occurs only when the other modes are inoperative (e.g. TMA-11) or in case of an urgent departure from the ISS. With a controlled descent, the actual landing location should be equally distributed around the target point, but it seems most of the landings occur NE of it, as if the landing was a bit "long".
What is the 'ET Disposal Problem'?
I believe you are right, it is the External Tank. Why does it have problems? The external tanks were deposited in either the Indian or Pacific Oceans, clear across the world. So, what would that do for a low southward inclination launch from Vandenburg? It would cut across South America, then over Africa, the Middle East, and Russia, with only a brief stay over the Atlantic and Pacific oceans.
My PCs have a plan that will get them all killed; how and why should I save them?
Let's simplify this scenario to what it amounts to: there's a button, and the players want to push it, and they're not sure what will happen, but you alone know that if they push it they die. Right now, you only see the option that they die. It is inescapable that character death tends to suck. You could explain they had no way of finding out — that would be terrible.
Are ICBMs and orbital launchers similar enough to be co-developed today?
It's not hypergolics per se that are super-desirable for ICBMs, but room-temperature-storable fuels. ICBMs have to stay ready for long periods of time and be launched on short notice, so that means they have to stay fueled up more or less constantly. In practice, that means solid fuels or something in the UDMH/NTO family. A cryogenic fuel ICBM would need hours of lead time before a launch.
Why do ion thrusters frequently use xenon as the reaction mass?
If everything operated ideally (it doesn't), the energy per particle would be given by $\Delta v^2 = 2\Delta E/m$. A larger particle mass results in a smaller velocity. The momentum per particle is given by $\Delta p = m\Delta v$, or $\Delta p = \sqrt{\Delta E m}$. Since the primary concern of electronic propulsion is imparting the maximum momentum to particles of gas, this strongly suggests that using a big particle is better. Note that this is diametrically opposed to chemical propulsion.
Why isn’t the “JRTI” barge larger?
I bet that's every rookie US Navy pilot's thought too on their first carrier landing approach. Thing is though, that unlike aircraft, Falcon 9 first stage can't really maintain altitude before landing. Even single of its nine Merlin engines throttled all the way down is too powerful for hovering on nearly empty tanks and landing is really going to be more of a Slam Dunk (a combination of Top Gun Arrival and Let Gravity Do It spot landing techniques).
How can I read the graph of a low pass filter
What does transfer or Vout/Vin mean, and why is it on the y-axis? Because I don't understand this, I can't understand the graph either... You could make the input signal \$V_{in}\$ anything that you want and solve for \$V_{out}\$. That's fine - it's just a bit of math. However, if you wanted to change \$V_{in}\$ to something else, then you'd have to re-calculate everything. You haven't learned anything; you've just solved the circuit for one signal.
What's inside NASA N911 Shuttle Carrier Aircraft (SCA 747)?
The Wikipedia article mentions that NASA's Boeing 747 Shuttle Carrier Aircraft (SCA 747) have the upstairs first class seating, and the rest of the plane was stripped bare. It doesn't mention anything going into the main fuselage, I'm guessing because nothing did go in. But is there anything? Given the limited fuel range of N911, I would wonder why the fuel tank wasn't expanded (too heavy, I presume). Bonus - why the heck is the plane escorted by unarmed FA18s when it has the orbiter on its back?
How weak can a propellant be and still get a rocket to space, theoretically?
There was, briefly, a discussion recently of the use of Mentos and Coke to get to space. It wasn't a serious question but pointed to a way of understanding the core of how rockets work. Last year I asked a variant of this and had enough trouble understanding the answers that I decided to leave it until I had seriously brushed up my math and physics.
What would one learn by borescoping a rocket engine after an aborted launch?
In November/December 2013, during the Falcon 9 Flight 7 (SES-8) processing flow, SpaceX managed to get the vehicle onto the pad and attempted to launch a few times without success. Either a scrub was called or the flight computers decided to automatically terminate the countdown prior to liftoff. During the second launch attempt "a slower-than-expected increase in pressure" (source) was seen on the first stage engines, and an abort was called by the flight computers at T-0.
What would one learn by boroscoping a rocket engine after an aborted launch?
In November/December 2013, during the Falcon 9 Flight 7 (SES-8) processing flow, SpaceX managed to get the vehicle onto the pad and attempted to launch a few times without success. Either a scrub was called or the flight computers decided to automatically terminate the countdown prior to liftoff. During the second launch attempt "a slower-than-expected increase in pressure" (source) was seen on the first stage engines, and an abort was called by the flight computers at T-0.
Can ion thrusters be scaled up?
Assuming you mean "quite small" in terms of mass as well as thrust output. Fundamentally, current ion drives are limited by the amount of power available to them - it takes many, many kilowatts of input power to provide tiny amounts of thrust. As you know from the answer you linked, the Dawn spacecraft is powered by 3 NSTAR ion engines which generate a maximum thrust of 90mN, and each has a mass itself of ~25.5kg.
How do I compress a folder with the Python GZip module?
I'm creating Python software that compresses files/folders... How would I create a section of the code that asks for the user input of the folder location and then compresses it. I currently have the code for a single file but not a folder full of files. Please explain in detail how to do this.
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