With the help of the Collecting Citadel Miniatures Group (I love how the prevailing mentality matches my own) I’ve discovered that the Rogue Trader Chaos backpacks are not at all jump packs. On top of Ian’s comment on the original post saharduin had this to say:
I’m afraid Ian Wood is correct in his comments at your blog. There was also at least one illustration of marines using regular backpacks as jump packs (Chapter Approved – the Book of the Astronomican) possibly also drawn by Ian Miller (I can’t recall for sure offhand and don’t have the book here to double-check).
There was also, to my immediate recollection, an illustration of squats holding their weapons upside down, and one of a marine holding his heavy weapon back to front. The point is, illustrators sometimes got things wrong.
There’s nothing to suggest that early Chaos backpacks were intended to be jump packs. They’re smaller than jump packs, they don’t look like jump packs, and they were catalogued as backpacks on every occasion. It’s weird that they had what looked like additional extended jets, but it seems to just have been a way to add stuff onto the existing imperial backpack designs to make them look more Chaos-y.
Greg
So I looked through the Book of the Astronomicon and found the illustration.

Nerd crisis over.













I have seen the picture in the Chapther Approved.
In the Rogue Trader rule book you find a picture of the Back-Pack.
The Back-Pack have to big jets (+2 Move) also Marine can fly with 4 Zoll horizontal or vertical.
http://images.wikia.com/warhammer40k/images/f/f3/Mk6corvuscompositiom.jpg
By StarQuest you can find a picture to on pge 13 in the Mission Book.