Mar 2009

Version 1.1 sent for review

This will be Satellites version 1.1 in the App Store -- sent to Apple today

+ added a second view, fixed centered on ISS

+ horizon ‘footprint’ reduced to 10 degrees

+ orbital track extended from 85 to 90 minutes into the future

+ azimuth/elevation of satellite shown when close to observer (in centered view only)

+ sluggish response after sleep/wake cycle fixed

Horizons are deceiving

Satellites has used a ‘horizon’ of zero degrees for the visibility footprint of ISS -- in other words, you could see it (and it could see you) immediately it rises over a perfectly flat horizon. In practice, this doesn’t happen unless the conditions are very, very clear, even if there are no trees or buildings in the way. Versions of Satellites hereafter will use a ten degree horizon, which is more reasonable. Geometry being what it is, the ten degree horizon footprint is nearly half the diameter of the zero degree one, so this will reduce false expectations of visibility when ISS stays lower than ten degrees off the horizon.

old Space Shuttle elements

I’ve noticed that Satellites has not shown the Space Station and the Shuttle in the same place for several days while they have been docked. Taking a closer look at the Shuttle orbital elements, I see they have not been updated at source for over 7 days (178 hours as I write this), while the ISS elements are less than a day old. I’m guessing that when the two are docked, the Shuttle elements don’t get updated, but there’s no way to tell this from the data.

Satellites shows the two orbiting objects just over a minute apart just now. Undocking should happen just before 4pm EDT on Wednesday 26th and then the two objects should start to drift apart.

We are on the App Store !

Apple OK’d Satellites for the App Store today!

Smoother transitions ...

Excellent suggestion from my buddy, plus the fact that the views flashed horribly when you went from the ‘celestial’ view to the ‘hovering’ view, plus the need to be able to swap in other views someday soon [hint: 3500 stars!] pushed me to understanding what UIViewControllers are good for. So we have a new version, with an animated view transition.

... best laid plans

Well, they got me! On the previous Shuttle flight the orbital elements named the object “STS-122” and so I coded Satellites to look for “STS-” in the name as the condition to show the orbit. The elements just published for the current Shuttle flight name the object “STS 119” -- no hyphen, so it doesn’t find it.

There’s a new download that fixes this.

Two in orbit !!

It’s a slight cheat but here’s ISS and the Shuttle. It’s a cheat because I took the pre-flight elements and edited them into the simulator’s data file by hand. NORAD updates its element sets twice a day so, unless the Shuttle is treated as a special case, it probably won’t show up till tomorrow (16th) morning. We’ll see.

Mar15/09 Release (Ad-Hoc v1.1)

While Apple considers the goodies recently placed in iTunes for their review, development marches on. A new ad-hoc version (which will be version 1.1 on the App Store) is available. As before, this version displays the orbital path of the International Space Station, but, if there is a Space Shuttle also in orbit, that will be plotted too.

With a possible launch of Discovery later today (Sunday 7:43pm EDT) on the STS-119 mission, this will be a good time to test this. The Space Shuttle will be plotted when it appears in the NORAD orbital element sets -- likely to be a couple of hours after launch.

It should be fun to watch the Shuttle catching up to the Space Station. If it launches on Sunday evening, they are expected to dock on Tuesday around 5:15pm EDT. When they are docked, the two tracks should exactly overlap (we’ll see!).

FYI: More information about STS-119 at
Spaceflight Now and, of course, NASA.

Approaching the Vernal Equinox

We are approaching the time when the Sun moves from illuminating mostly the southern hemisphere to mostly the northern hemisphere -- from March 20th, the northern days are longer than the nights.

Even if we get a blizzard in April, the Spring will have begun!

Satellites, the illuminated hemisphere of the Earth, as presented in the first screen before any manipulation, as seen here, will all be in view (and the dark hemisphere all invisible). Vernal Equinox marks two transitions -- one we’ve just mentioned, when the ‘latitude’ of the Sun passes zero degrees heading north, the other is the Sun passing through zero degrees of celestial ‘longitude’ (or Right Ascension).

Satellites initial frame of reference places the observer at the zero points on both these axes, at the Vernal Equinox the user of Satellites has exactly the same view of the Earth that the Sun does, and we can’t see any of the Earth’s shadow.


I had to change the name of the product to “Satellites” so it wasn’t truncated on the iPhone screen. So there is a new Ad-Hoc release on the downloads page. Note that download contains a new provisioning file that you’ll need to drop on iTunes for the application to load onto your iPhone/iTouch.

This is the first version submitted to the iTunes App Store.

Mar01/09 Release

There’s a new ad-hoc version of Satellite Tracker available.

This version has two screens, as a precursor to a third screen yet to be coded. The first screen, the one we’ve had all along, displays the Earth with the ISS rotating around it. The second reverses this view and keeps the ISS in the center of the screen while the Earth rotates under it.

The views are toggled back and forth with the circular button on the bottom left of the screen.