Timeline for How do spaceships determine each other's mass in space?
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 11, 2019 at 15:04 | comment | added | Luaan | @JohnDvorak Certainly. Though it should be noted that photons are great for fuel efficiency, but not thrust - you need a lot of power for a miniscule amount of thrust. The only way to use lasers for efficient space propulsion would be with an outside power source - e.g. beaming arrays. Otherwise you're better off just throwing mass out of your ship fast, and it's a lot cheaper too. But anyway, it's not like you can have the magical sensors that most soft sci-fi ships have; you just need something that works for the situations you're likely to find yourself in. | |
| Mar 11, 2019 at 14:57 | comment | added | John Dvorak | @Luaan this won't work if you use invisible exhaust, like photons or the good ole sterile neutrinos. And photons in particular are a great exhaust because they are blazingly fast. | |
| Mar 11, 2019 at 14:35 | comment | added | Luaan | @AndrzejDoyle But even your varying efficiency argument has a huge problem - the efficiency range just isn't going to be that wide. You can get some idea about the kind of engine the target ship is using, and get a reasonably slim efficiency range. Even 20%-80% is far more precise than your unrealistic 0.1%-0.01% figure; in reality, the variation is probably going to be much smaller, especially if the target ship isn't some enigmatic alien or high-performance stealth gunship fresh from the drawing boards. | |
| Mar 11, 2019 at 14:26 | comment | added | Luaan | @AndrzejDoyle Actually, it's even simpler than that - don't look at the engines, look at the exhaust. You can compare the size and temperature of the exhaust with the acceleration you observe and get a very accurate reading on the ship's mass, especially if you have a book of known engine configurations etc. (as WWII ships had for identifying enemy ships; but unlike those, you can't fake your exhaust in space - the difference between a merchant and a warship will always be obvious, especially if you rely on armor rather than some magic shields for protection). | |
| Mar 11, 2019 at 14:24 | comment | added | Luaan | @JohnDvorak Yes, but if we're talking about intra-system travel, CMBR probably is not a big deal - unless in an emergency, you'd probably accelerate at 1g or less to keep reasonable comfort for the pilot and doubly so for any passengers. Other than that, definitely the best way to get around space without FTL as soon as you have a torchdrive. | |
| Mar 9, 2019 at 18:31 | comment | added | John Dvorak | @Kepotx "instantly accelerate, coast the whole way, instantly decelerate" is only optimal if you want to conserve as much fuel as possible (and even then that discounts the utility of an Oberth maneuver). If you want to get somewhere as fast as possible, you want to constantly accelerate for one half of the trip, and decelerate for the other half. Do be advised though that once you get fast enough, CMBR in front of you gets blue-shifted back to the gamma range, and the occasional hydrogen atom will become troublesome even sooner, let alone stray rocks. | |
| Mar 7, 2019 at 23:32 | comment | added | GrandmasterB | I think this is basically what modern military aircraft do. Simple, effective, and if you add a couple hundred years of AI advancement, should be extremely accurate. | |
| Mar 7, 2019 at 21:39 | comment | added | Luke | #2 is what we currently use for massing small things like asteroids. Except, we can't always measure the size directly. We often estimate the size based on the brightness. It's the worst option for accuracy, but the most commonly used. | |
| Mar 7, 2019 at 14:37 | comment | added | Burki | Your first point is the most likely one, imho: check Wikipedia. | |
| Mar 7, 2019 at 13:08 | comment | added | vsz | @Kepotx : for that, you need to know the origin and destination of the ship. | |
| Mar 7, 2019 at 11:58 | comment | added | Andrzej Doyle | I'm not convinced that point 3 necessarily works - the ratio of "wasted" radiation to useful energy could vary wildly (0.1% loss vs 0.01% loss would mean your mass calcs are out by a factor of ten). Plus it's not a given that this radiates equally in all directions, so even calculating the total waste from a sample would be difficult. It would probably be more feasible to simply measure the velocity and mass flow of the exhaust, which gives you the precise acceleration force - and hence, very trivially, the mass of the ship. | |
| Mar 7, 2019 at 11:57 | comment | added | Separatrix | Adding to the troubles with point 2, if you look at the vibrations of the overall vessel you may be able to estimate how full it is and the mass of the cargo. A laser microphone should be able to do this if their engines are running. | |
| Mar 7, 2019 at 10:37 | comment | added | Kepotx | By full speed, I didn't mean max speed allowed by laws of physics, but optimal speed, as the faster you go, the more you have to break. Also, making maneuver consume energy, so you want to avoid it if possible. | |
| Mar 7, 2019 at 10:31 | comment | added | DarthDonut | @Kepotx I fear there is no such thing as "full speed" in space other than light speed. Sure, if you are on a set course without the need to maneuver, point 3 does not work. And for a cargo ship, you could still get lower and upper bounds of possible masses. | |
| Mar 7, 2019 at 10:26 | comment | added | Kepotx | wouldn't point 3 work only on areas impacted by gravity, as once you are on space, you don't need to accelerate anymore (at least if you already are on full speed) | |
| Mar 7, 2019 at 10:22 | comment | added | Kepotx | good answer, but point 2 may be hard to apply for cargo ship, as their mass also depend on how full they are and what goods they have on board. | |
| Mar 7, 2019 at 9:53 | history | answered | DarthDonut | CC BY-SA 4.0 |