Created by Paul Allinger, Roger Stern, and Lawrence Rosler.
Designed to show two-suited hands when interfering over opponents' 1NT opening.
2C = at least 5-4 shape with 5 Hearts plus one minor suit.
2D = 5-4 shape with at least 5 Spades plus another suit (could be hearts).
Responses -- Responder bids
a. 2 of known major with 3 card support or better
b. Cheapest step response to denies three cards in the known major.
c. Two spades or three clubs to show at least a 6 card suit and denies support for the known major.
d. Two notrump is the only forcing response, asking bidder to show second suit. This requires a minimum of 10 points.
e. Raise of the Astro overcall shows a good 6 card suit, denies the major suit support, and invites game.
f. Jump in any suit is natural and invites game.
g. A game bid is sign off.
Where the Astro overcall is doubled, partner may
a. pass to show 4 cards in the overcall suit or
b. make normal response.