Newton's second law states that force is proportional to mass. If 100 metric tons of water are added to ISS, the thrust would be increased by (520/420)-1, or 23.8%. The additional push can be garnered either by a stronger push or by pushing longer. Newton's second law is typically expressed as F=ma, but since we can make the substitution a=v/t and then solve for t, the equation becomes t=mv/F. for a constant force, more time is required as mass is increased. Does that make sense? Brent On Thursday, March 5, 2015 8:10 AM, Seth Jarvis <SJarvis@slco.org> wrote: How much would be necessary to do it with 100 tons of water layered around the crew areas for radiation protection? -----Original Message----- From: Utah-Astronomy [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Brent Watson via Utah-Astronomy Sent: Thursday, February 26, 2015 3:45 PM To: Richard Tenney; Utah Astronomy; Utah Astronomy Subject: Re: [Utah-astronomy] Last night's lecture Joe, Well, that was fun! I just made some calculations to answer your question. It was fun manipulating Newton's second law to get the answer and then comparing that answer to the Saturn 5 rocket. Joe we don't have to lift it from the earth's surface. We have to lift it from the Earth's orbit to Mars' orbit. Not a trivial task. But here are the answers you asked for - if my math is correct. We have to add between 4 km/sec and 6 km/sec according to Mr. Adamo for a reasonable transfer orbit. That is between 8,950 and 13,424 miles per hour! We then have to lose that velocity on the other end. Actually, because the gravity of Mars is less than that of the earth we will have to lose more, but we'll ignore that for right now. If we were to use the Saturn 5 1st stage, we would require a burn of between 47 an 70 seconds on both ends. The Saturn 5 rocket could only be ignited once. It could not be stopped and then relighted. That is a total burn of between 94 and 140 seconds. The Saturn 5 first stage burn time was 165 seconds. Of course, we would have to get the Saturn 5 first stage into orbit and rendezvous with ISS. The Saturn 5 first stage had a mass of 2290 metric tons. That is beyond the capabilities of even the Saturn 5 let alone anything we have or are designing today. Of course it could be done with more than one trip, but we're talking about more than half the mass of ISS that took several dozen trips to complete. Ok, how about the second stage? Using the thrust available there we would require a burn time of between 354 and 545 seconds on each end. Total burn time would be between 11.8 minutes and 18.2 minutes. It was designed to burn for only 360 seconds (6 minutes), and could not be re-started. That's out. Ok, a smaller rocket. The Saturn 3rd stage. That would require a burn on each end of between 1600 and 2400 seconds. Total burn time would be between 53 minutes and 80 minutes. The third stage could be restarted, but could only burn for 165 seconds and then again for 335 seconds. As you can see, to send ISS to Mars is a pretty large order. We have, nor have we ever had anything that would do the job. Nor has any other country. If I am not mistaken, the Saturn 5 was the largest rocket ever to grace the earth. There is nothing that compares to it today, nor is anything on the drawing boards. It is also evident that the Saturn 5 is a very bad match to this task. We would need to build a vehicle that is much better tailored to the requirements of this mission. I hope this answers your question. Brent On Thursday, February 26, 2015 2:46 PM, Richard Tenney via Utah-Astronomy <utah-astronomy@mailman.xmission.com> wrote: Pshaw, like in the classic movie The Thing (John Carpenter version), once Chuck is done taking inventory of and organizing all the cool stuff in his basement, we'll just have him assemble an interplanetary transporter; problem solved without all the heavy lifting. From: Seth Jarvis <SJarvis@slco.org> To: 'Utah Astronomy' <utah-astronomy@mailman.xmission.com> Sent: Thursday, February 26, 2015 2:28 PM Subject: Re: [Utah-astronomy] Last night's lecture This question has prompted 15 minutes of nerdgasm among several of our staff. Looks like the "delta-v" necessary to transition from Low Earth Orbit to a bare-bones transfer orbit to Mars is a skosh under 5 km/sec. Long story short, if you magically decree that the 420,000 kg ISS is structurally capable of undergoing the acceleration achievable by real-world chemical rockets, and also magically provision the ISS for a 20-month round-trip crewed mission, and then magically shield it to protect its crew from the radiation received in interplanetary space, all without increasing its mass (hence the need for magic) then you'd need to find a way to strap four or five sets of Space Shuttle boosters, main engines and Hydrogen/Oxygen fuel tanks (i.e., everything but the shuttle orbiter itself) to the ISS if your goal is the accelerate the ISS and send it to Mars. (And if you want a Mars landing vehicle and a habitat for astronauts while they wait for the ISS's next visit, that's extra.) And just how do you get four or five completely fueled sets of Space Shuttle rockets into Low Earth Orbit? Ummmm... Seth -----Original Message----- From: Utah-Astronomy [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Thursday, February 26, 2015 12:49 PM To: daniel turner; Utah Astronomy Subject: Re: [Utah-astronomy] Last night's lecture Daniel, you just beat me to it. The ISS is still traveling well below escape velocity. On Thu, Feb 26, 2015 at 12:46 PM, daniel turner via Utah-Astronomy < utah-astronomy@mailman.xmission.com> wrote:
Joe: Low earth orbit is still deep inside the gravity well of the planet earth. In terms of energy the ISS is only halfway to achieving an orbit around the sun. It's still a long way uphill to get anywhere. DT
Brent, Your answer touched on an issue I don't fully understand. How much thrust would it take to nudge the ISS, which is already in orbit, into another orbit that would sligshot it toward Mars? It's not as if we need to lift it into space. Thanks, Joe
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