Robotech is one of the most-beloved cartoons of the '80s and a pillar of American anime fandom, yet it can barely make a sequel to save its life. It's not for a lack of trying; owner Harmony Gold has tried to produce new Robotech TV series and movies for decades with almost no success.
1) Robotech II: The Sentinels
The first intended sequel to the original Robotech series was a 65-episode series titled The Sentinels, which began to be produced in 1986. But only three episodes, serving as a sort of feature-length pilot, even got animated. The show was going to combine Robotech's three sagas — Macross, Southern Cross and Next Generation (each originally culled from a different anime series and edited together to create Robotech) — although the series would take place more or less at the same timeframe as Next Generation. In the show, Rick Hunter, Lasa Hayes and other Macross characters would be joined by Dana Sterling and Bowie Grant from Southern Cross, taking a new Super-Dimensional Fortress into space to combat both the Robotech Masters and the Invid. According to Robotech mastermind Carl Macek, when the dollar/yen exchanged rate plummeted in the mid-'80s, the project became too expensive for Robotech toy producer Matchbox, and the project was canceled.
2) Robotech III: The Odyssey
This second Robotech sequel never made it past the proposal stage, and thus existed entirely in Macek's mind. It was completely insane, even by the loose standards of '80s anime. This new series would have taken place after Sentinels — the non-existent Sentinels — and featured the Macross/Southern Cross characters on the SDF-3 going back in time, becoming the Robotech Masters, and eventually making the original Super-Dimensional Fortress that would crash-land on Earth in the very first Robotech episode, which of course kicked off the entire series. Furthermore, Minmei (best known as the underage Chinese pop star who mercilessly toys with Rick Hunter's affection in Macross) would give birth to Zor, the Master who created the Protoculture that fueled all Robotechnology, and who sent the SDF-1 to Earth just before his death. Madness.
3) Robotech 3000
In 2000, Macek tried again, planning a new cartoon that would utilize the CG that seemed to be so popular with the kids. The show was set in 2999 with an all-new crew, ship, and whatever the hell was mutating and controlling corrupted mecha. Robotech fans just hated it, mostly because it was CG and not the classic anime style of the original, but it didn't matter because the CG production company Nutter Digital went bankrupt not long after the above demo footage was created, and the project was scrapped. Macek and Harmony Gold then worked on a Robotech direct-to-DVD movie titled Shadow Chronicles, directed by Tommy Yune, which actually did manage to get fully made and released, albeit seven years later.
4) Robotech: Shadow Rising
Of course, since Shadow Chronicles did get released, Harmony Gold planned to follow it up with another direct-to-DVD movie. It was announced by Yune at the 2007 San Diego Comic-Con, and other than its title and the fact it was originally supposed to come out in 2009, virtually nothing is known about it. Supposedly it's been postponed because of the omnipresent threat of a live-action Robotech movie, but who knows. However, at the 2013 Comic-Con, Yune suggested that Shadow Rising may still come out in 2015. I wouldn't hold your breath.
5) Robotech Academy
Announced on July 5th at this year's Anime Expo, the proposed series Robotech Academy is currently only a Kickstarter project and one that has earned only $166,000 of its $500,000 goal, with just 16 more days to go. So Robotech Academy hasn't officially failed yet, but it's not looking good. If somehow fans do get their shit (and their checkbooks) together, the series would be set at the same time as the (still completely non-existent) Sentinels series, and would feature a new generation of young characters in a combination training academy/Robotechnology research center, which is attacked by the Children of Zor, a cult of aliens who want the protoculture stored in said Academy. But then the Academy is accidentally transported across the galaxy, much like in the original Macross saga. Even if the Kickstarter's goal is reached, this would only fund a pilot — so turning that into a full-fledged Academy series would be another battle entirely, not to mention a much more difficult one.