Posted by Rory on Wednesday, December 28, 2011 at 10:59pm.
change of altitude: 205-60=145
rule of thumb: deletV=145mile*2/sec.mile
290ft/sec
I see that someone else is in the VASTS program that didn't understand this problem...
But I might add that that would be the necessary velocity to do it, but the question asks for the CHANGE in velocity. The change in velocity would be 290ft/sec - (the initial) 2ft/sec, so 288 ft/sec.
isn't that wrong because of the units?
you would have to convert 145 mi to 765,600 ft.
then divide by 2 (because its 2 ft/s) and get 382,800.
then subtract 2 ft/s to get the change, so 382,798.
is that right or did i do something wrong?
I too am in VASTS... that's what I thought. The units would have to be converted first to feet to get an answer in ft/sec.
I am also in the program, but I was wondering did you guys use the program to help you at all?
My computer is really slow and I've only been able to get it to work once...
Some hard stuff homie.
How can you find Delta V without having the initial Velocity?
Thank you all for your help, but I'm still confused, I converted miles to feet
145 miles= 765600 feet
then what?
If you divide 765600 by 2 ft/sec you're going to still have a huge number. I don't think that's right somehow. I'm going to get a teacher's help today.
if you take 1 and at the answer minus 1 it is correct
*add
or did i mean subtract?
ok im leaving now hahahahaha bye
The first one I believe is right except for the units. Since 2 ft/sec is just rule of thumb, it wouldn't count towards the change. That's just the information given so that 2ft/sec = 1 mile. If you have 145 miles, for every mile you're going 2 ft/sec. So you would multiply 145 times 2.
what is the initial velocity? how can you find the Delta v without the initial
I'm so glad I'm not the only one lost in VASTS. What a relief!
Eh, from what it looks like, it should just be the change in height that you need to do, which will be in units of miles right? and then you multiply that by the ratio of delta V to altitude change, which I believe is in units of (ft/s)/(change in miles)
Ughhh this is confusing. - In the VASTS program. I'm just glad I'm not the only one having trouble :P
I am also in the VASTS program.My data is different, but they have the same concept.
This is the same question that HAS is using. I'm happy that I'm not the only one who needs help with it.
u guys area bunch of cheaters
I'm struggling with this ... Can anyone help me?
I'm pretty sure it would be 290 feet per second
no 290 miles per second
You would convert 290 miles into 1531200 ft which then the answer would be a531200 ft/sec
I am in the WAS program and we have a similar question with different values. How I think it works is much like the first answer. You find the change in perigee needed. Its 205 right now but needs to be 60. So 205-60 is 145 MILES. This is the distance that needs to be changed. Because the rule is 2 ft/s for every mile we do not need to change the units, we have 145 miles and need to change 2 ft/s for each of those miles. So we multiply by 2 and get 290 ft/s. The final thing to consider is that the change is slowing the craft ad not speeding it up so the delta V would be negative and not positive. Making your final answer -290 ft/s.
I hope this helps/is correct and doesn't confuse further.
i hate vasts
R = 6378000 meters
a₁ = R + (212 miles + 246 miles)/2
a₁ = 6746540 meters
a₂ = R + 60 miles
a₂ = 6474561 meters
GMₑ = 3.986e14 m³ sec⁻²
Energy per unit mass in present orbit.
E₁/m = −GMₑ/(2a₁)
E₁/m = −29541068 J
Energy per unit mass in destination orbit.
E₂/m = −GMₑ/(2a₂)
E₂/m = −30782010 J
|ΔE|/m = 1240942 J
½ (Δv)² = 1240942 J
Δv = 1575.4 m/s
Julie, could you elaborate the last step to find the change in velocity? I followed until the very end where you got 1575.4.
Nevermind, I figured it out :)
Vasts sucks balls
lol ryan wtf, do you understand this cuz i dont, does the apogee even matter? cuz noone has mentioned it above