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Old 11-23-2017, 07:12 AM   #46
Keatah
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..thought mathematics was a universal language. And thus should be written and understood in one way only.
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Old 11-23-2017, 10:08 AM   #47
Urwumpe
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Originally Posted by 4throck View Post
 To be pedantic, on my mother tongue the correct way to write 1000 with decimals (on a price for example) is:

1.000,00

Same in German. I suspect it has something to do with the medieval history of Europe.

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Old 11-23-2017, 10:47 AM   #48
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Quote:
..thought mathematics was a universal language. And thus should be written and understood in one way only.
The language is universal, its alphabet certainly not.

Quote:
1.000,00
We're a little less ambiguous in Switzerland:
1'000,0
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Old 11-23-2017, 09:59 PM   #49
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Strange, I found no english wiki article about Francesco Pellos, he has written the "Sen segue de la art de arithmeticha es semblātment de ieumetria dich ho nominatz Cōpendiō de lo abaco" in which as far as we know today, the point has been used first as a decimal delimiter.
Maybe somebody wants to create an english wiki article, I think he would deserved it... ;-)

Last edited by Topper; 11-23-2017 at 10:07 PM.
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Old 11-24-2017, 04:19 AM   #50
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One thing I've seen in older British texts is the use of a mid-dot as a decimal point, which makes it look to non-British eyes like multiplication, e.g:

1,00000
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Old 11-24-2017, 02:05 PM   #51
4throck
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Originally Posted by Topper View Post
 "Sen segue de la art de arithmeticha es semblātment de ieumetria dich ho nominatz Cōpendiō de lo abaco"
Had to look that up, because it didn't seem like old spanish or latin, and it isn't! It's Occitan language

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Old 11-25-2017, 06:47 PM   #52
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An interesting thought I've had:

Previous estimates on the density of comets in interstellar space had been based on the assumption that a hyperbolic object passing through the solar system would be cometary in nature (would develop a coma and tail), and would thus be easily detectable. What if 'Oumuamua is not atypical? What if most interstellar objects are in fact asteroidal in nature, or if a comet needs to make a few passes close to a star to "activate" (for example, if fracturing from heating and cooling is needed to create sufficient outgassing area or something). That could significantly affect the detectability of interstellar objects and significantly change the densities we might calculate from our observations. Strangely, I haven't really seen a lot of discussion of this possibility.
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Old 12-01-2017, 05:23 PM   #54
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Originally Posted by boogabooga View Post
 My initial instinct on seeing this was skepticism that something interstellar would have come this close to the sun. And since velocities are so low in Oort cloud, it is possible for collisions, etc. to put comets on hyperbolic trajectories. But, if you run the numbers, e= 1.2 at 0.25 AU perihelion gives V infinity of about 25,500 m/s, and nothing in Oort Cloud is moving that fast, or could be reasonably expected to accelerate to that speed.

The universe must be crawling with comets.
I'm also puzzled by the coincidence that it traveled so close to the Sun. Of course if some alien civilization wanted to spend more time in the Solar System ...


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Old 12-01-2017, 05:42 PM   #55
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Originally Posted by RGClark View Post
 I'm also puzzled by the coincidence that it traveled so close to the Sun. Of course if some alien civilization wanted to spend more time in the Solar System ...


Bob Clark
I suspect that we have a bias at only detecting those that gt close to US, and WE are the ones that are close to the sun...
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Old 12-02-2017, 06:06 PM   #56
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Originally Posted by boogabooga View Post
 I suspect that we have a bias at only detecting those that gt close to US, and WE are the ones that are close to the sun...
On the other hand, if you wanted to get particularly close to an interesting planet ...


---------- Post added at 10:16 PM ---------- Previous post was at 09:57 PM ----------

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Originally Posted by Tex View Post

Very well done. Great narration.



---------- Post added 12-02-17 at 01:06 PM ---------- Previous post was 12-01-17 at 10:16 PM ----------

The proposed "Project Lyra" to the interstellar asteroid is discussed here:

Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid.
https://arxiv.org/abs/1711.03155

I was surprised though they only considered chemical and solar sail propulsion, and not ion propulsion. Ion propulsion has already been used for NASA missions to get high velocity space probes.

Oumuamua had a velocity of about 25 km/s. The ion drive on the Dawn mission to Ceres could manage 10 km/s.

As discussed on this forum about the New Horizons mission it got a mission cruise speed of about 12 km/s as launched by the Atlas V with added in-space stages. So you would need an additional 13 km/s to match the speed of Oumuamua. This could be reached by putting some larger propellant tanks on the Dawn probe. Actually, NASA frequently makes duplicates of their spacecraft for testing purposes, so there may be an extra Dawn spacecraft already available.

The Dawn spacecraft is about 3 times larger than New Horizons so you would need a larger launcher than the Atlas V to attain the same departure delta-v. The upgraded version the Falcon Heavy probably could do it. The SLS certainly could.

Bob Clark

Last edited by RGClark; 12-02-2017 at 06:10 PM.
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Old 12-03-2017, 12:56 AM   #57
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We should get an Orbiter scenario together with Oumuamua on its trajectory, then the community can experiment for itself as sees fit.

Where can one obtain accurate orbital elements?

Would it be better to model it as a spacecraft or 'on the rails' as a solar system object? Can Orbiter even handle solar system objects on hyperbolic trajectories?
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Old 12-03-2017, 01:07 PM   #58
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Originally Posted by boogabooga View Post
 We should get an Orbiter scenario together with Oumuamua on its trajectory, then the community can experiment for itself as sees fit.
Where can one obtain accurate orbital elements?
Would it be better to model it as a spacecraft or 'on the rails' as a solar system object? Can Orbiter even handle solar system objects on hyperbolic trajectories?
We need to know how far away Oumuamua is also. Even if we can match it's speed, if it's too far away, it will take too long to catch up to it. Heil et.al. summarized their proposals on Centauiri-dreams.org here:

Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (formerly A/2017 U1), the Interstellar Asteroid
by PAUL GILSTER on NOVEMBER 10, 2017
Quote:
As shown previously, chasing 1I/‘Oumuamua with a realistic launch date (next 5-10 years), is a formidable challenge for current space systems. Adam Crowl (i4is) and Marshall Eubanks (Asteroid Initiatives LLC) have pondered a single launch architecture. Nominally a single launch architecture, via the Space Launch System (SLS) for example, would simplify mission design. However other launch providers project promising capabilities in the next few years. One potential mission architecture is to make use of SpaceX’s Big Falcon Rocket (BFR) and their in-space refueling technique with a launch date in 2025. To achieve the required hyperbolic excess (at least 30 km/s) a Jupiter flyby combined with a close solar flyby (down to 3 solar radii), nicknamed “solar fryby” is envisioned. This maneuver is also known under “Oberth Maneuver” [5]. The architecture is based on the Keck Institute for Space Studies (KISS) [6] and the Jet Propulsion Laboratory (JPL) [7] interstellar precursor mission studies. Using the BFR however eliminates the need for multi-planet flybys to build up momentum for a Jupiter trajectory. Instead via direct launch from a Highly Eccentric Earth Orbit (HEEO) the probe, plus various kick-stages, is given a C3 of 100 km/s into an 18 month trajectory to Jupiter for a gravity assist into the solar fryby. A multi-layer thermal shield protects the spacecraft, which is boosted by a high-thrust solid rocket stage at perihelion. The KISS Interstellar Medium study computed that a hyperbolic excess velocity of 70 km/s was possible via this technique, a value which achieves an intercept at about 85 AU in 2039 for a 2025 launch. More modest figures can still fulfill the mission, such as 40 km/s with an intercept at 155 AU in 2051. With the high approach speed a hyper-velocity impactor to produce a gas ‘puff’ to sample with a mass spectrometer could be the serious option to get in-situ data.
https://www.centauri-dreams.org/?p=3...comment-166728

The high speeds mentioned there, which have the advantage of using only chemical propulsion, are necessitated by having to wait for the needed planetary alignments for gravitational assists. This means Oumuamua will be even farther away and we'll need high speed to catch up with it. That also means we will only be able to do a flyby.

On the other hand, being able to launch within a year or so using currently existing craft means the distance to be crossed is shorter and not as high a speed will be needed. That also means a smaller speed will need to be killed off and an actual landing may be possible.

Bob Clark

Last edited by RGClark; 12-03-2017 at 01:14 PM.
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Old 12-03-2017, 05:19 PM   #59
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Originally Posted by RGClark View Post
 We need to know how far away Oumuamua is also.
When you have orbital elements at an Epoch, you can predict position as a function of time.
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Old 12-03-2017, 09:23 PM   #60
4throck
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Don't know it this is exactly what you are looking for but the orbital elements are here:

https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2017U1;cad=1
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