For the sake of their mission, some alterations were made to the Bifrost. They needed one that can be opened from both sides, unless they wanted to risk getting stuck, of course. The new portal was one equipped into a large space ship like aircraft that doubled as an operation base as well. It carried all the equipment the Valkyries needed in addition to great stealth capabilities so there was little risk of the enemy finding it, unless they have more advanced tech, which is to be expected of a bunch claiming to be from a higher realm.
Once they arrived on the other side Sam found the most optimal place to land and had the Valkyries prepare to start the investigation. First of all he sent out a swarm of drones to scan the surrounding area and a small satellite to get a wider range. Once he was sure there is no danger in their immediate vicinity he went out to take a look for himself.
"That's one small step for man, one giant leap for mankind."